In 1800, the population of Japan was just over 30 million, a figure which would grow by just two million in the first half of the 19th century. However, with the fall of the Tokugawa shogunate and the restoration of the emperor in the Meiji Restoration of 1868, Japan would begin transforming from an isolated feudal island, to a modernized empire built on Western models. The Meiji period would see a rapid rise in the population of Japan, as industrialization and advancements in healthcare lead to a significant reduction in child mortality rates, while the creation overseas colonies would lead to a strong economic boom. However, this growth would slow beginning in 1937, as Japan entered a prolonged war with the Republic of China, which later grew into a major theater of the Second World War. The war was eventually brought to Japan's home front, with the escalation of Allied air raids on Japanese urban centers from 1944 onwards (Tokyo was the most-bombed city of the Second World War). By the war's end in 1945 and the subsequent occupation of the island by the Allied military, Japan had suffered over two and a half million military fatalities, and over one million civilian deaths.

The population figures of Japan were quick to recover, as the post-war “economic miracle” would see an unprecedented expansion of the Japanese economy, and would lead to the country becoming one of the first fully industrialized nations in East Asia. As living standards rose, the population of Japan would increase from 77 million in 1945, to over 127 million by the end of the century. However, growth would begin to slow in the late 1980s, as birth rates and migration rates fell, and Japan eventually grew to have one of the oldest populations in the world. The population would peak in 2008 at just over 128 million, but has consistently fallen each year since then, as the fertility rate of the country remains below replacement level (despite government initiatives to counter this) and the country's immigrant population remains relatively stable. The population of Japan is expected to continue its decline in the coming years, and in 2020, it is estimated that approximately 126 million people inhabit the island country.

In 1938, the year before the outbreak of the Second world War, the countries with the largest populations were China, the Soviet Union, and the United States, although the United Kingdom had the largest overall population when it's colonies, dominions, and metropole are combined. Alongside France, these were the five Allied "Great Powers" that emerged victorious from the Second World War. The Axis Powers in the war were led by Germany and Japan in their respective theaters, and their smaller populations were decisive factors in their defeat. Manpower as a resource In the context of the Second World War, a country or territory's population played a vital role in its ability to wage war on such a large scale. Not only were armies able to call upon their people to fight in the war and replenish their forces, but war economies were also dependent on their workforce being able to meet the agricultural, manufacturing, and logistical demands of the war. For the Axis powers, invasions and the annexation of territories were often motivated by the fact that it granted access to valuable resources that would further their own war effort - millions of people living in occupied territories were then forced to gather these resources, or forcibly transported to work in manufacturing in other Axis territories. Similarly, colonial powers were able to use resources taken from their territories to supply their armies, however this often had devastating consequences for the regions from which food was redirected, contributing to numerous food shortages and famines across Africa, Asia, and Europe. Men from annexed or colonized territories were also used in the armies of the war's Great Powers, and in the Axis armies especially. This meant that soldiers often fought alongside their former-enemies. Aftermath The Second World War was the costliest in human history, resulting in the deaths of between 70 and 85 million people. Due to the turmoil and destruction of the war, accurate records for death tolls generally do not exist, therefore pre-war populations (in combination with other statistics), are used to estimate death tolls. The Soviet Union is believed to have lost the largest amount of people during the war, suffering approximately 24 million fatalities by 1945, followed by China at around 20 million people. The Soviet death toll is equal to approximately 14 percent of its pre-war population - the countries with the highest relative death tolls in the war are found in Eastern Europe, due to the intensity of the conflict and the systematic genocide committed in the region during the war.

Throughout the Common Era, Japan's population saw relatively steady growth between each century. Failed invasions and distance from Asia's mainland meant that Japan was unaffected by many pandemics, primarily bubonic plague, therefore its development was not drastically impeded in the same way as areas such as China or Europe. Additionally, religious practices meant that hygiene was prioritized much more in Japan than in other regions, and dietary customs saw lower rates of meat consumption and regular boiling of water in meals or tea; both of these factors contributed to lower rates of infection for many parasitic or water-borne diseases. Fewer international conflicts and domestic stability also saw lower mortality in this regard, and Japan was an considered an outlier by Asian standards, as some shifting trends associated with the demographic transition (such as lower child mortality and fertility) began taking place in the 17th century; much earlier time than anywhere else in the world. Yet the most significant changes came in the 20th century, as Japan's advanced healthcare and sanitation systems saw drastic reductions in mortality. Challenges Japan's isolation meant that, when pandemics did arrive, the population had less protection and viruses could have higher mortality rates; smallpox has been cited as the deadliest of these pandemics, although increased international contact in the late 19th century brought new viruses, and population growth slowed. Earlier isolation also meant that crop failure or food shortages could leave large sections of the population vulnerable, and, as mentioned, the Japanese diet contained relatively little meat, therefore there was a higher reliance on crops and vegetables. It is believed that the shortage of arable land and the acidity of the soil due to volcanic activity meant that agriculture was more challenging in Japan than on the Asian mainland. For most of history, paddy fields were the most efficient source of food production in Japan, but the challenging nature of this form of agriculture and changes in employment trends gradually led to an increased reliance in imported crops. Post-Sakoku Japan Distance from the Asian mainland was not the only reason for Japan's isolation; from 1603 to 1853, under the Tokugawa shogunate, international trade was restricted, migration abroad was forbidden, and most foreign interaction was centered around Nagasaki. American neo-imperialism then forced Japan to open trade with the west, and Japan became an imperial power by the early-1900s. Japanese expansion began with a series of military victories against China and Russia at the turn of the century, and the annexation of Taiwan, Korea, and Manchuria by the 1930s, before things escalated further during its invasion of China and the Second World War. Despite its involvement in so many wars, the majority of conflicts involving Japan were overseas, therefore civilian casualties were much lower than those suffered by other Asian countries during this time. After Japan's defeat in 1945, its imperial ambitions were abandoned, it developed strong economic ties with the West, and had the fastest economic growth of any industrial country in the post-WWII period. Today, Japan is one of the most demographically advanced countries in the world, with the highest life expectancy in most years. However, its population has been in a steady decline for over a decade, and low fertility and an over-aged society are considered some of the biggest challenges to Japanese society today.

Japan Population Census: Male: Age 25 to 29 Years data was reported at 3,255,717.000 Person in 2015. This records a decrease from the previous number of 3,691,723.000 Person for 2010. Japan Population Census: Male: Age 25 to 29 Years data is updated yearly, averaging 3,875,527.000 Person from Dec 1920 (Median) to 2015, with 20 observations. The data reached an all-time high of 5,426,289.000 Person in 1975 and a record low of 1,603,664.000 Person in 1945. Japan Population Census: Male: Age 25 to 29 Years data remains active status in CEIC and is reported by Statistical Bureau. The data is categorized under Global Database’s Japan – Table JP.G002: Population: Annual.

It is estimated that the Second World War was responsible for the deaths of approximately 3.76 percent of the world's population between 1939 and 1945. In 2022, where the world's population reached eight billion, this would be equal to the death of around 300 million people.

The region that experienced the largest loss of life relative to its population was the South Seas Mandate - these were former-German territories given to the Empire of Japan through the Treaty of Versailles following WWI, and they make up much of the present-day countries of the Marshall Islands, Micronesia, the Northern Mariana Islands (U.S. territory), and Palau. Due to the location and strategic importance of these islands, they were used by the Japanese as launching pads for their attacks on Pearl Harbor and in the South Pacific, while they were also taken as part of the Allies' island-hopping strategy in their counteroffensive against Japan. This came at a heavy cost for the local populations, a large share of whom were Japanese settlers who had moved there in the 1920s and 1930s. Exact figures for both pre-war populations and wartime losses fluctuate by source, however civilian losses in these islands were extremely high as the Japanese defenses resorted to more extreme measures in the war's final phase.

Japan Population Census: Male: Age 30 to 34 Years data was reported at 3,684,747.000 Person in 2015. This records a decrease from the previous number of 4,221,011.000 Person for 2010. Japan Population Census: Male: Age 30 to 34 Years data is updated yearly, averaging 3,849,696.500 Person from Dec 1920 (Median) to 2015, with 20 observations. The data reached an all-time high of 5,421,545.000 Person in 1980 and a record low of 1,805,587.000 Person in 1945. Japan Population Census: Male: Age 30 to 34 Years data remains active status in CEIC and is reported by Statistical Bureau. The data is categorized under Global Database’s Japan – Table JP.G002: Population: Annual.

The median age of the population in Japan has steadily been increasing since 1950 and is projected to be around 47.7 years old in 2020. As of 2021, the median age of Japan is the second highest in the world, behind the Principality of Monaco. The elderly in Japan An improved quality of life and regular health checks are just two reasons why Japan has one of the highest life expectancies in the world. The life expectancy from birth in Japan improved significantly after World War II, rising 20 years in the decade between 1945 and 1955. As life expectancy continues to increase, Japan expects difficulties caring for the older generation in the future. Shortages in the service sector are already a major concern, with demand for nurses and care workers increasing. Fertility and birth rates The fertility rate among Japan’s population has been around 1.4 children per woman since 2010. Apart from a small baby boom in the early seventies, the crude birth rate of Japan has been declining since 1950 and is expected to be as low as 7.5 births per thousand people in 2020. With falling birth rates and such a large share of its inhabitants reaching their later years, Japan’s total population is expected to continue declining.

By August 1945, U.S. and British Commonwealth forces had pushed the Japanese back through Southeast Asia to the Japanese mainland, while Japanese control in China was weakening each day, and the Soviet Union was rapidly approaching from the west. However, despite inevitable defeat looming over the Empire of Japan, its military leaders encouraged its forces to fight to the death, and Japanese resistance grew in ferocity as they were pushed back to the mainland, most notably on the islands of Iwo Jima and Okinawa. As U.S. leadership realized that an amphibious assault on the Japanese mainland would result in heavy and unnecessary casualties on both sides, including large numbers of civilians, an alternative measure was sought. The USSR's advance also put time pressure on the Americans, as defeating Japan quickly would give the U.S. more time to assert control over the region, without having to split control with the Soviets (as was the case in Germany). The bombs are dropped On May 31, 1945, it was suggested that the U.S. demonstrate the power of the atomic bomb to the Japanese, to convince them to surrender - the plan was rejected, however, in the fear that it was not convincing enough, that the Japanese may shoot down the plane, or that the bomb was a dud - instead, a surprise attack was viewed as the most effective course of action. Following the Trinity Test in July 16, the United States achieved the goal of successfully creating and detonating a nuclear weapon. On July 26, the leaders of the U.S., UK, and China all called for the unconditional surrender of Japan, otherwise Japan would face "prompt and utter destruction". Japan did not surrender, and on the morning of August 6, the Enola Gay B-29 bomber dropped an atomic bomb, known as "Little Boy", over the city of Hiroshima. Japan still refused to surrender, and three days later, another bomb, known as "Fat Man", was dropped over Nagasaki. Japan's surrender was announced on August 15, and formalized on September 2, 1945, bringing WWII to a close. Impact The bomb dropped over Hiroshima was a uranium 235 bomb, which detonated at approximately 580 meters (1,900ft) above the ground and had a yield of 16 kilotons (i.e. it had the same blast force as 16,000 tons of TNT). The bomb dropped over Nagasaki was a plutonium 239 bomb, which detonated at approximately 500 meters (1,650ft) and had a yield of 21 kilotons. The temperatures at the epicenter of the explosions reached around 3,000-4,000 degrees Celsius, and thermal radiation was so strong that it caused third degree burns over a kilometer from ground zero. The majority of those within a one km radius of both explosions were killed instantly through the blast force and intense heat, while those further away were more susceptible to injuries by burning, falling debris and glass, and radiation. Additionally, as the fallout from the blast (i.e. radioactive dust and ash sent into the air by the explosion) returned to the ground it was carried by the wind to populations outside of the blast radius, and radiation sickness then took hold over the days and weeks that followed. Due to the nature of the attack, Japan's population distribution at the time, and the long-term effects of radiation poisoning (which may be responsible for illnesses and death several years after exposure), there is no accepted consensus on the total number of deaths due to the atomic bombings at Hiroshima and Nagasaki -the figures given appear to be on the lower end of estimate ranges, where combined estimates generally vary between 110,000 and 210,000 deaths.

The fertility rate of a country is the average number of children that women from that country will have throughout their reproductive years. From 1800 until 1865, Japan's fertility rate grew quite gradually, from 4.1 children per woman, to 4.8. From this point the fertility rate drops to 3.6 over the next ten years, as Japan became more industrialized. Towards the end of the nineteenth century, Japan's fertility rate grew again, and reached it's highest recorded point in the early 1920s, where it was 5.4 children per woman. Since this point it has been gradually decreasing until now, although it did experience slight increases after the Second World War, and in the early 1970s. In recent decades Japan's population has aged extensively, and today, Japan has the second oldest population and second highest life expectancy in the world (after Monaco). In contrast to this, Japan has a very low birth rate, and it's fertility rate is expected to fall below 1.4 children per woman in 2020.

In 1800, it is estimated that approximately 9.4 million people lived in the region of modern-day South Korea (and 13.8 million on the entire peninsula). The population of this region would remain fairly constant through much of the 19th century, but would begin to grow gradually starting in the mid-1800s, as the fall of the Joseon dynasty and pressure from the U.S. and Japan would end centuries of Korean isolationism. Following the opening of the country to foreign trade, the Korean peninsula would begin to modernize, and by the start of the 20th century, it would have a population of just over ten million. The Korean peninsula was then annexed by Japan in 1910, whose regime implemented industrialization and modernization policies that saw the population of South Korea rising from just under ten million in 1900, to over fifteen million by the start of the Second World War in 1939.

The Korean War Like most regions, the end of the Second World War coincided with a baby boom, that helped see South Korea's population grow by almost two million between 1945 and 1950. However, this boom would stop suddenly in the early 1950s, due to disruption caused by the Korean War. After WWII, the peninsula was split along the 38th parallel, with governments on both sides claiming to be the legitimate rulers of all Korea. Five years of tensions then culminated in North Korea's invasion of the South in June 1950, in the first major conflict of the Cold War. In September, the UN-backed South then repelled the Soviet- and Chinese-backed Northern army, and the frontlines would then fluctuate on either side of the 38th parallel throughout the next three years. The war came to an end in July, 1953, and had an estimated death toll of three million fatalities. The majority of fatalities were civilians on both sides, although the North suffered a disproportionate amount due to extensive bombing campaigns of the U.S. Unlike North Korea, the South's total population did not fall during the war.

Post-war South Korea Between the war's end and the late 1980s, the South's total population more than doubled. In these decades, South Korea was generally viewed as a nominal democracy under authoritarian and military leadership; it was not until 1988 when South Korea transitioned into a stable democracy, and grew its international presence. Much of South Korea's rapid socio-economic growth in the late 20th century was based on the West German model, and was greatly assisted by Japanese and U.S. investment. Today, South Korea is considered one of the world's wealthiest and most developed nations, ranking highly in terms of GDP, human development and life expectancy; it is home to some of the most valuable brands in the world, such as Samsung and Hyundai; and has a growing international cultural presence in music and cinema. In the past decades, South Korea's population growth has somewhat slowed, however it remains one of the most densely populated countries in the world, with total population of more than 51 million people.

人口普查：男性：年龄25至 29岁在12-01-2015达3,255,717.000人，相较于12-01-2010的3,691,723.000人有所下降。人口普查：男性：年龄25至 29岁数据按年更新，12-01-1920至12-01-2015期间平均值为3,875,527.000人，共20份观测结果。该数据的历史最高值出现于12-01-1975，达5,426,289.000人，而历史最低值则出现于12-01-1945，为1,603,664.000人。CEIC提供的人口普查：男性：年龄25至 29岁数据处于定期更新的状态，数据来源于総務省 統計局，数据归类于Global Database的日本 – 表 JP.G002：人口：年度。

During the Second World War, the three Axis powers of Germany, Italy, and Finland mobilized the largest share of their male population. For the Allies, the Soviet Union mobilized the largest share of men, as well as the largest total army of any country, but it was restricted in its ability to mobilize more due to the impact this would have on its economy. Other notable statistics come from the British Empire, where a larger share of men were drafted from Dominions than from the metropole, and there is also a discrepancy between the share of the black and white populations from South Africa.

However, it should be noted that there were many external factors from the war that influenced these figures. For example, gender ratios among the adult populations of many European countries was already skewed due to previous conflicts of the 20th century (namely WWI and the Russian Revolution), whereas the share of the male population eligible to fight in many Asian and African countries was lower than more demographically developed societies, as high child mortality rates meant that the average age of the population was much lower.

In 1800, the population of Indonesia was estimated to be approximately 16 million. The population of the island nation would grow steadily over the course of the 19th century, as the Dutch colonial administration launched several initiatives to modernize the region. After reaching 38 million people in 1900, the population of Indonesia would continue to grow until the 1940’s, when the Japanese occupation of the country would see between four to ten million Indonesians moved away from the island nation to be made to work on Japanese military projects, and in combination with wartime famine, this would result in the death or displacement of up to four million Indonesians by the end of the Japanese occupation in 1945. Despite this, Indonesia's population continued to grow throughout these years.

Following the Second World War, Indonesia claimed its independence from the Netherlands, and achieved this in 1949. In the second half of the 20thcentury, the population would continue to grow exponentially in size through the remainder of the 20th century, although the growth rate would slow somewhat in the 1980s, the result of a decline in fertility rate throughout the country which some studies suggest may be attributed to improved access to birth control and improved mass education. In 2020, Indonesia is estimated to have just over 273.5 million people living within its borders, making it the fourth most populous country in the world (behind the U.S. and above Pakistan).

In Japan, the crude birth rate in 1800 was 29.6 live births per thousand people, meaning that approximately three percent of the population had been born in that year. From 1800 to 1865, Japan's crude birth rate rose gradually to around 34 births per thousand people, before dropping relatively sharply to 25 over the next ten years. This was a time of great social and economic reform in Japan, as the country became increasingly urbanized and industrialized. Japan's crude birth rate reached it's highest recorded point in the early 1920s, where the number was almost 35 births per thousand people, and since then it has been decreasing gradually. There were two times in the twentieth century where Japan's crude birth rate increased, after the Second World War, and during the period of economic prosperity in the 1960s and 70s. Since 1975, Japan's crude birth rate has gradually decreased to it's lowest recorded rate ever, and is expected to be at just 7.5 births per thousand people in 2020, making it the second lowest in the world (behind Monaco).

The Empire of Japan's military losses in the Second World War are estimated to exceed 2.5 million men. For Japan, the costliest front in the Pacific theater was the battle against the United States in the Philippines, closely followed by its invasion of China, known as the Second Sino-Japanese War. After 1941, the Imperial Japanese Army was simultaneously stretched across several frontlines in the Pacific theater, and this was one contributing factor to their eventual defeat as reinforcing and supplying various armies across these fronts was unfeasible in the long-term.

Estimates for the total death count of the Second World War generally range somewhere between 70 and 85 million people. The Soviet Union suffered the highest number of fatalities of any single nation, with estimates mostly falling between 22 and 27 million deaths. China then suffered the second greatest, at around 20 million, although these figures are less certain and often overlap with the Chinese Civil War. Over 80 percent of all deaths were of those from Allied countries, and the majority of these were civilians. In contrast, 15 to 20 percent were among the Axis powers, and the majority of these were military deaths, as shown in the death ratios of Germany and Japan. Civilian deaths and atrocities It is believed that 60 to 67 percent of all deaths were civilian fatalities, largely resulting from war-related famine or disease, and war crimes or atrocities. Systematic genocide, extermination campaigns, and forced labor, particularly by the Germans, Japanese, and Soviets, led to the deaths of millions. In this regard, Nazi activities alone resulted in 17 million deaths, including six million Jews in what is now known as The Holocaust. Not only was the scale of the conflict larger than any that had come before, but the nature of and reasoning behind this loss make the Second World War stand out as one of the most devastating and cruelest conflicts in history. Problems with these statistics Although the war is considered by many to be the defining event of the 20th century, exact figures for death tolls have proven impossible to determine, for a variety of reasons. Countries such as the U.S. have fairly consistent estimates due to preserved military records and comparatively few civilian casualties, although figures still vary by source. For most of Europe, records are less accurate. Border fluctuations and the upheaval of the interwar period mean that pre-war records were already poor or non-existent for many regions. The rapid and chaotic nature of the war then meant that deaths could not be accurately recorded at the time, and mass displacement or forced relocation resulted in the deaths of many civilians outside of their homeland, which makes country-specific figures more difficult to find. Early estimates of the war’s fatalities were also taken at face value and formed the basis of many historical works; these were often very inaccurate, but the validity of the source means that the figures continue to be cited today, despite contrary evidence.

In comparison to Europe, estimate ranges are often greater across Asia, where populations were larger but pre-war data was in short supply. Many of the Asian countries with high death tolls were European colonies, and the actions of authorities in the metropoles, such as the diversion of resources from Asia to Europe, led to millions of deaths through famine and disease. Additionally, over one million African soldiers were drafted into Europe’s armies during the war, yet individual statistics are unavailable for most of these colonies or successor states (notably Algeria and Libya). Thousands of Asian and African military deaths went unrecorded or are included with European or Japanese figures, and there are no reliable figures for deaths of millions from countries across North Africa or East Asia. Additionally, many concentration camp records were destroyed, and such records in Africa and Asia were even sparser than in Europe. While the Second World War is one of the most studied academic topics of the past century, it is unlikely that we will ever have a clear number for the lives lost in the conflict.

Life expectancy in Japan was 36.4 in the year 1860, and over the course of the next 160 years, it is expected to have increased to 84.4, which is the second highest in the world (after Monaco). Although life expectancy has generally increased throughout Japan's history, there were several times where the rate deviated from its previous trajectory. These changes were a result of the Spanish Flu in the 1910s, the Second World War in the 1940s, and the sharp increase was due to the high rate of industrialization and economic prosperity in Japan, in the mid-twentieth century.

The Second World War was fought on such a large scale that it became total war in many countries - this is where the war effort is prioritized above all else, and the entire population and economy are mobilized to support all military endeavors. Germany and Japan were committing over 70 percent of their national income to the war effort in its final years.

There were also notable fluctuations that coincided with major events for corresponding powers. These included the UK's mobilization of its defenses in 1940, after Germany took most of Western Europe; the spike in Soviet military spending after Operation Barbarossa in June, 1941; and the U.S. entry into the war following the Pearl Harbor attacks in December, 1941.

The Second World War had a sever impact on gender ratios across European countries, particularly in the Soviet Union. While the United States had a balanced gender ratio of one man for every woman, in the Soviet Union the ratio was below 5:4 in favor of women, and in Soviet Russia this figure was closer to 4:3.

As young men were disproportionately killed during the war, this had long-term implications for demographic development, where the generation who would have typically started families in the 1940s was severely depleted in many countries.

In the build up to the Second World War, the United States was the major power with the highest gross domestic product (GDP) per capita in the world. In 1938, the United States also had the highest overall GDP in the world, and by a significant margin, however differences in GDP per person were much smaller. Switzerland In terms of countries that played a notable economic role in the war, the neutral country of Switzerland had the highest GDP per capita in the world. A large part of this was due to the strength of Switzerland's financial system. Most major currencies abandoned the gold standard early in the Great Depression, however the Swiss Franc remained tied to it until late 1936. This meant that it was the most stable, freely convertible currency available as the world recovered from the Depression, and other major powers of the time sold large amounts of gold to Swiss banks in order to trade internationally. Switzerland was eventually surrounded on all sides by Axis territories and lived under the constant threat of invasion in the war's early years, however Swiss strategic military planning and economic leverage made an invasion potentially more expensive than it was worth. Switzerland maintained its neutrality throughout the war, trading with both sides, although its financial involvement in the Holocaust remains a point of controversy. Why look at GDP per capita? While overall GDP is a stronger indicator of a state's ability to fund its war effort, GDP per capita is more useful in giving context to a country's economic power in relation to its size and providing an insight into living standards and wealth distribution across societies. For example, Germany and the USSR had fairly similar GDPs in 1938, whereas Germany's per capita GDP was more than double that of the Soviet Union. Germany was much more industrialized and technologically advanced than the USSR, and its citizens generally had a greater quality of life. However these factors did not guarantee victory - the fact that the Soviet Union could better withstand the war of attrition and call upon its larger population to replenish its forces greatly contributed to its eventual victory over Germany in 1945.