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.

PERIOD: 1920-1939. NOTE: (As of October 1st but as of September 1st in 1923)The population estimates were obtained as follows: (1) For 1921 to 1923, the population estimate is the sum of county- and city-level population estimates obtained by multiplying the de facto population in the Population Census conducted on October 1, 1920, with the average annual population growth rate by gender from 1908 to 1918. (2) For 1924, the difference between the population of Japan overall calculated using the population growth rate by sex in each city and summing up the results and the population overall calculated using the population growth rate by sex for Japan overall was proportionally subtracted from the population of each prefecture; moreover, the population decrease due to the Great Kanto Earthquake on September 1, 1923 was also taken into account. (3) For Taisho 1926 to 1929, the de facto population in the 1920 and 1925 Population Censuses is used to obtain the annual average geometric growth rate of Japan's population overall, which is then used to estimate the population. (4) For 1931 to 1934, the same procedure is employed using the de facto population in the 1920 and 1930 Population Censuses. (5) From 1926 onward, the population estimates are obtained by adding the increase in the difference between births and deaths up to each estimation year in the 1935 Population Census using the results of the Vital Statistics survey. SOURCE: [Survey by the Statistics Bureau, Imperial Cabinet].

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.

PERIOD: Oct. 1, 1930. SOURCE: Population Census of Japan; [Survey by the Statistics Bureau, Imperial Cabinet].

PERIOD: Oct. 1, 1935. SOURCE: Population Census of Japan; [Survey by the Statistics Bureau, Imperial Cabinet].

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.

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.

Those residing in Japan as of 0:00h, civilians in military employ residing abroad, etc.

PERIOD: Oct. 1, 1930. NOTE: The unemployed are classified based on their last occupation before becoming unemployed. SOURCE: Population Census of Japan; [Survey by the Statistics Bureau, Imperial Cabinet].

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.

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 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).

Male: Total, Male: 0-4 years old, Male: 5-9 years old, Male: 10-14 years old, Male: 15-19 years old, Male: 20-24 years old, Male: 25-29 years old, Male: 30-34 years old, Male: 35-39 years old, Male: 40-44 years old, Male: 45-49 years old, Male: 50-54 years old, Male: 55-59 years old, Male: 60 and over, Female: Total, Female: 0-4 years old, Female: 5-9 years old, Female: 10-14 years old, Female: 15-19 years old, Female: 20-24 years old, Female: 25-29 years old, Female: 30-34 years old, Female: 35-39 years old, Female: 40-44 years old, Female: 45-49 years old, Female: 50-54 years old, Female: 55-59 years old, Female: 60 and over, Both Sexes

Total, Age 0, Age 1, Age 2, Age 3, Age 4, Age 5, Age 6, Age 7, Age 8, Age 9, Age 10, Age 11, Age 12, Age 13, Age 14, Age 15, Age 16, Age 17, Age 18, Age 19, Age 20, Age 21, Age 22, Age 23, Age 24, Age 25, Age 26, Age 27, Age 28, Age 29, Age 30, Age 31, Age 32, Age 33, Age 34, Age 35, Age 36, Age 37, Age 38, Age 39, Age 40, Age 41, Age 42, Age 43, Age 44, Age 45, Age 46, Age 47, Age 48, Age 49, Age 50, Age 51, Age 52, Age 53, Age 54, Age 55, Age 56, Age 57, Age 58, Age 59, Age 60, Age 61, Age 62, Age 63, Age 64, Age 65, Age 66, Age 67, Age 68, Age 69, Age 70, Age 71, Age 72, Age 73, Age 74, Age 75, Age 76, Age 77, Age 78, Age 79, Age 80, Age 81, Age 82, Age 83, Age 84, Age 85 and over

Over the course of the Second World War approximately 127.2 million people were mobilized. The world's population in 1940 was roughly 2.3 billion, meaning that between five and six percent of the world was drafted into the military in some capacity. Approximately one in every 25 people mobilized were women, who generally served in an administrative or medical role, although hundreds of thousands of women did see active combat. Largest armies In absolute numbers, the Soviet Union mobilized the largest number of people at just under 34.5 million, and this included roughly 35 percent of the USSR's male population. By the war's end, more Soviets were mobilized than all European Axis powers combined. However, in relative terms, it was Germany who mobilized the largest share of its male population, with approximately 42 percent of men serving. The USSR was forced to find a balance between reinforcing its frontlines and maintaining agricultural and military production to supply its army (in addition to those in annexed territory after 1941), whereas a large share of soldiers taken from the German workforce were replaced by workers drafted or forcibly taken from other countries (including concentration camp prisoners and PoWs). Studying the figures The figures given in these statistics are a very simplified and rounded overview - in reality, there were many nuances in the number of people who were effectively mobilized for each country, their roles, and their status as auxiliary, collaborative, or resistance forces. The British Empire is the only power where distinctions are made between the metropole and its colonies or territories, whereas breakdowns of those who fought in other parts of Asia or Africa remains unclear. Additionally, when comparing this data with total fatalities, it is important to account for the civilian death toll, i.e. those who were not mobilized.

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.

PERIOD: Korea, Taiwan, South Sakhalin and Kwantung Province, 1930-1939 year-end. South Pacific Mandate, every October 1 from 1930 to 1937 and 1938-1939 year-end. NOTE: Excluding local troops each places. SOURCE: [Survey by the Statistics Bureau, Imperial Cabinet; Statistics by government offices, overseas territories of Japan].

For most of the Second World War, the Soviet Union had the largest number of active military personnel each year, peaking at over 12 million people in the war's final years. The Soviet Union's ability to draw from its larger population was decisive in its eventual victory over Germany in 1945, whose eastern forces were greatly diminished by 1944 after it had already suffered heavy losses fighting the Soviets and was then forced to fight on the western front.

Each of the Great Powers had varying conscription systems in place that allowed them to draft citizens into the military. In the U.S., over 50 million men aged 18-45 would register for the draft before the war's end, and over 10 million of these were inducted into the military (alongside volunteers and those already in service). Conscription in Japan grew more aggressive as the war progressed, and its armed forces doubled in size in the final two years of the war.

In 1900, the crude birth rate in South Korea was just under 42 births for every thousand people, meaning that approximately 4.2 percent of the population was born in that year. The crude birth rate would rise briefly in the 1930s, as Japanese investment would lead to economic growth on the peninsula, but would fall sharply in the 1940s, as the Second World War and the Korean War would result in two decades of significant socio-economic turmoil. While the crude birth rate would recover quickly after the end of the Korean War in 1953, a sharp decline in fertility beginning in the 1960s would see a corresponding fall in the crude birth rate lasting until the late 1980s, as South Korea would go through a rapid demographic transition and modernization. While the crude birth rate would briefly rise in the early 1990s, partially due to governmental restrictions on sex-selective abortion; the rate of decline would slow going into the 21st century. As a result, in 2020, it is estimated that South Korea has a birth rate of seven births for every thousand people, which is one of the lowest birth rates in the world.

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.