The world's population first reached one billion people in 1805, and reached eight billion in 2022, and will peak at almost 10.2 billion by the end of the century. Although it took thousands of years to reach one billion people, it did so at the beginning of a phenomenon known as the demographic transition; from this point onwards, population growth has skyrocketed, and since the 1960s the population has increased by one billion people every 12 to 15 years. The demographic transition sees a sharp drop in mortality due to factors such as vaccination, sanitation, and improved food supply; the population boom that follows is due to increased survival rates among children and higher life expectancy among the general population; and fertility then drops in response to this population growth. Regional differences The demographic transition is a global phenomenon, but it has taken place at different times across the world. The industrialized countries of Europe and North America were the first to go through this process, followed by some states in the Western Pacific. Latin America's population then began growing at the turn of the 20th century, but the most significant period of global population growth occurred as Asia progressed in the late-1900s. As of the early 21st century, almost two-thirds of the world's population lives in Asia, although this is set to change significantly in the coming decades. Future growth The growth of Africa's population, particularly in Sub-Saharan Africa, will have the largest impact on global demographics in this century. From 2000 to 2100, it is expected that Africa's population will have increased by a factor of almost five. It overtook Europe in size in the late 1990s, and overtook the Americas a few years later. In contrast to Africa, Europe's population is now in decline, as birth rates are consistently below death rates in many countries, especially in the south and east, resulting in natural population decline. Similarly, the population of the Americas and Asia are expected to go into decline in the second half of this century, and only Oceania's population will still be growing alongside Africa. By 2100, the world's population will have over three billion more than today, with the vast majority of this concentrated in Africa. Demographers predict that climate change is exacerbating many of the challenges that currently hinder progress in Africa, such as political and food instability; if Africa's transition is prolonged, then it may result in further population growth that would place a strain on the region's resources, however, curbing this growth earlier would alleviate some of the pressure created by climate change.

In the past four centuries, the population of the Thirteen Colonies and United States of America has grown from a recorded 350 people around the Jamestown colony in Virginia in 1610, to an estimated 346 million in 2025. While the fertility rate has now dropped well below replacement level, and the population is on track to go into a natural decline in the 2040s, projected high net immigration rates mean the population will continue growing well into the next century, crossing the 400 million mark in the 2070s. Indigenous population Early population figures for the Thirteen Colonies and United States come with certain caveats. Official records excluded the indigenous population, and they generally remained excluded until the late 1800s. In 1500, in the first decade of European colonization of the Americas, the native population living within the modern U.S. borders was believed to be around 1.9 million people. The spread of Old World diseases, such as smallpox, measles, and influenza, to biologically defenseless populations in the New World then wreaked havoc across the continent, often wiping out large portions of the population in areas that had not yet made contact with Europeans. By the time of Jamestown's founding in 1607, it is believed the native population within current U.S. borders had dropped by almost 60 percent. As the U.S. expanded, indigenous populations were largely still excluded from population figures as they were driven westward, however taxpaying Natives were included in the census from 1870 to 1890, before all were included thereafter. It should be noted that estimates for indigenous populations in the Americas vary significantly by source and time period. Migration and expansion fuels population growth The arrival of European settlers and African slaves was the key driver of population growth in North America in the 17th century. Settlers from Britain were the dominant group in the Thirteen Colonies, before settlers from elsewhere in Europe, particularly Germany and Ireland, made a large impact in the mid-19th century. By the end of the 19th century, improvements in transport technology and increasing economic opportunities saw migration to the United States increase further, particularly from southern and Eastern Europe, and in the first decade of the 1900s the number of migrants to the U.S. exceeded one million people in some years. It is also estimated that almost 400,000 African slaves were transported directly across the Atlantic to mainland North America between 1500 and 1866 (although the importation of slaves was abolished in 1808). Blacks made up a much larger share of the population before slavery's abolition. Twentieth and twenty-first century The U.S. population has grown steadily since 1900, reaching one hundred million in the 1910s, two hundred million in the 1960s, and three hundred million in 2007. Since WWII, the U.S. has established itself as the world's foremost superpower, with the world's largest economy, and most powerful military. This growth in prosperity has been accompanied by increases in living standards, particularly through medical advances, infrastructure improvements, clean water accessibility. These have all contributed to higher infant and child survival rates, as well as an increase in life expectancy (doubling from roughly 40 to 80 years in the past 150 years), which have also played a large part in population growth. As fertility rates decline and increases in life expectancy slows, migration remains the largest factor in population growth. Since the 1960s, Latin America has now become the most common origin for migrants in the U.S., while immigration rates from Asia have also increased significantly. It remains to be seen how immigration restrictions of the current administration affect long-term population projections for the United States.

Japan Population Census: Age 20 to 24 Years data was reported at 5,968,127.000 Person in 2015. This records a decrease from the previous number of 6,426,433.000 Person for 2010. Japan Population Census: Age 20 to 24 Years data is updated yearly, averaging 7,822,781.000 Person from Dec 1920 (Median) to 2015, with 20 observations. The data reached an all-time high of 10,727,636.000 Person in 1970 and a record low of 4,609,310.000 Person in 1920. Japan Population Census: Age 20 to 24 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.

Ukraine Population Distribution: with Avg Income per Capita: Under 1920 UAH data was reported at 6.900 % in 2017. This records a decrease from the previous number of 18.400 % for 2016. Ukraine Population Distribution: with Avg Income per Capita: Under 1920 UAH data is updated yearly, averaging 53.150 % from Dec 2010 (Median) to 2017, with 8 observations. The data reached an all-time high of 78.100 % in 2010 and a record low of 6.900 % in 2017. Ukraine Population Distribution: with Avg Income per Capita: Under 1920 UAH data remains active status in CEIC and is reported by State Statistics Service of Ukraine. The data is categorized under Global Database’s Ukraine – Table UA.H009: Household Income and Expenditure: Annual.

PERIOD: World total, circa 1920. SOURCE: [Statistics and reports of major countries].

Japan Population Census: Age 50 to 54 Years data was reported at 7,930,296.000 Person in 2015. This records an increase from the previous number of 7,644,499.000 Person for 2010. Japan Population Census: Age 50 to 54 Years data is updated yearly, averaging 4,766,430.500 Person from Dec 1920 (Median) to 2015, with 20 observations. The data reached an all-time high of 10,441,990.000 Person in 2000 and a record low of 2,234,762.000 Person in 1920. Japan Population Census: Age 50 to 54 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.

Japan Population Census: Male: Age 50 to 54 Years data was reported at 3,968,311.000 Person in 2015. This records an increase from the previous number of 3,809,576.000 Person for 2010. Japan Population Census: Male: Age 50 to 54 Years data is updated yearly, averaging 2,179,935.000 Person from Dec 1920 (Median) to 2015, with 20 observations. The data reached an all-time high of 5,210,038.000 Person in 2000 and a record low of 1,122,240.000 Person in 1920. Japan Population Census: Male: Age 50 to 54 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.

Japan Population Census: Age 25 to 29 Years data was reported at 6,409,612.000 Person in 2015. This records a decrease from the previous number of 7,293,701.000 Person for 2010. Japan Population Census: Age 25 to 29 Years data is updated yearly, averaging 7,743,240.500 Person from Dec 1920 (Median) to 2015, with 20 observations. The data reached an all-time high of 10,794,583.000 Person in 1975 and a record low of 3,923,949.000 Person in 1920. Japan Population Census: 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.

Japan Population Census: Age 15 to 64 Years data was reported at 76,288,736.000 Person in 2015. This records a decrease from the previous number of 81,031,800.000 Person for 2010. Japan Population Census: Age 15 to 64 Years data is updated yearly, averaging 69,781,671.000 Person from Dec 1920 (Median) to 2015, with 20 observations. The data reached an all-time high of 87,164,721.000 Person in 1995 and a record low of 32,605,495.000 Person in 1920. Japan Population Census: Age 15 to 64 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.

PERIOD: World total, circa 1920. SOURCE: [Statistics and reports of major countries].

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: Female: Age 20 to 24 Years data was reported at 2,921,735.000 Person in 2015. This records a decrease from the previous number of 3,160,193.000 Person for 2010. Japan Population Census: Female: Age 20 to 24 Years data is updated yearly, averaging 3,906,815.500 Person from Dec 1920 (Median) to 2015, with 20 observations. The data reached an all-time high of 5,382,751.000 Person in 1970 and a record low of 2,292,831.000 Person in 1920. Japan Population Census: Female: Age 20 to 24 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 region of present-day China has historically been the most populous region in the world; however, its population development has fluctuated throughout history. In 2022, China was overtaken as the most populous country in the world, and current projections suggest its population is heading for a rapid decline in the coming decades. Transitions of power lead to mortality The source suggests that conflict, and the diseases brought with it, were the major obstacles to population growth throughout most of the Common Era, particularly during transitions of power between various dynasties and rulers. It estimates that the total population fell by approximately 30 million people during the 14th century due to the impact of Mongol invasions, which inflicted heavy losses on the northern population through conflict, enslavement, food instability, and the introduction of bubonic plague. Between 1850 and 1870, the total population fell once more, by more than 50 million people, through further conflict, famine and disease; the most notable of these was the Taiping Rebellion, although the Miao an Panthay Rebellions, and the Dungan Revolt, also had large death tolls. The third plague pandemic also originated in Yunnan in 1855, which killed approximately two million people in China. 20th and 21st centuries There were additional conflicts at the turn of the 20th century, which had significant geopolitical consequences for China, but did not result in the same high levels of mortality seen previously. It was not until the overlapping Chinese Civil War (1927-1949) and Second World War (1937-1945) where the death tolls reached approximately 10 and 20 million respectively. Additionally, as China attempted to industrialize during the Great Leap Forward (1958-1962), economic and agricultural mismanagement resulted in the deaths of tens of millions (possibly as many as 55 million) in less than four years, during the Great Chinese Famine. This mortality is not observable on the given dataset, due to the rapidity of China's demographic transition over the entire period; this saw improvements in healthcare, sanitation, and infrastructure result in sweeping changes across the population. The early 2020s marked some significant milestones in China's demographics, where it was overtaken by India as the world's most populous country, and its population also went into decline. Current projections suggest that China is heading for a "demographic disaster", as its rapidly aging population is placing significant burdens on China's economy, government, and society. In stark contrast to the restrictive "one-child policy" of the past, the government has introduced a series of pro-fertility incentives for couples to have larger families, although the impact of these policies are yet to materialize. If these current projections come true, then China's population may be around half its current size by the end of the century.

Japan Population Census: Male: Age 35 to 39 Years data was reported at 4,204,202.000 Person in 2015. This records a decrease from the previous number of 4,950,122.000 Person for 2010. Japan Population Census: Male: Age 35 to 39 Years data is updated yearly, averaging 3,859,640.500 Person from Dec 1920 (Median) to 2015, with 20 observations. The data reached an all-time high of 5,398,230.000 Person in 1985 and a record low of 1,707,771.000 Person in 1920. Japan Population Census: Male: Age 35 to 39 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.

At the beginning of the 19th century, the area of modern-day Italy, at the time a collection of various states and kingdoms, was estimated to have a population of nineteen million, a figure which would grow steadily throughout the century, and by the establishment of the Kingdom of Italy in 1861, the population would rise to just over 26 million.

Italy’s population would see its first major disruption during the First World War, as Italy would join the Allied Forces in their fight against Austria-Hungary and Germany. In the First World War, Italy’s population would largely stagnate at 36 million, only climbing again following the end of the war in 1920. While Italy would also play a prominent role in the Second World War, as the National Fascist Party-led country would fight alongside Germany against the Allies, Italian fatalities from the war would not represent a significant percentage of Italy’s population compared to other European countries in the conflict. As a result, Italy would exit the Second World War with a population of just over 45 million.

From this point onwards the Italian economy started to recover from the war, and eventually boomed, leading to increased employment and standards of living, which facilitated steady population growth until the mid-1980s, when falling fertility and birth rates would cause growth to largely cease. From this point onward, the Italian population would remain at just over 57 million, until the 2000s when it began growing again due to an influx of migrants, peaking in 2017 at just over 60 million people. In the late 2010s, however, the Italian population began declining again, as immigration slowed and the economy weakened. As a result, in 2020, Italy is estimated to have fallen to a population of 59 million.

The total fertility rate of the world has dropped from around 5 children per woman in 1950, to 2.2 children per woman in 2025, which means that women today are having fewer than half the number of children that women did 75 years ago. Replacement level fertility This change has come as a result of the global demographic transition, and is influenced by factors such as the significant reduction in infant and child mortality, reduced number of child marriages, increased educational and vocational opportunities for women, and the increased efficacy and availability of contraception. While this change has become synonymous with societal progress, it does have wide-reaching demographic impact - if the global average falls below replacement level (roughly 2.1 children per woman), as is expected to happen in the 2050s, then this will lead to long-term population decline on a global scale. Regional variations When broken down by continent, Africa is the only region with a fertility rate above the global average, and, alongside Oceania, it is the only region with a fertility rate above replacement level. Until the 1980s, the average woman in Africa could expect to have 6-7 children over the course of their lifetime, and there are still several countries in Africa where women can still expect to have 5 or more children in 2025. Historically, Europe has had the lowest fertility rates in the world over the past century, falling below replacement level in 1975. Europe's population has grown through a combination of migration and increasing life expectancy, however even high immigration rates could not prevent its population from going into decline in 2021.

Japan Population Census: Age 30 to 34 Years data was reported at 7,290,878.000 Person in 2015. This records a decrease from the previous number of 8,341,497.000 Person for 2010. Japan Population Census: Age 30 to 34 Years data is updated yearly, averaging 7,681,689.000 Person from Dec 1920 (Median) to 2015, with 20 observations. The data reached an all-time high of 10,771,731.000 Person in 1980 and a record low of 3,609,450.000 Person in 1920. Japan Population Census: 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.

In 1800, the population of the region of present-day India was approximately 169 million. The population would grow gradually throughout the 19th century, rising to over 240 million by 1900. Population growth would begin to increase in the 1920s, as a result of falling mortality rates, due to improvements in health, sanitation and infrastructure. However, the population of India would see it’s largest rate of growth in the years following the country’s independence from the British Empire in 1948, where the population would rise from 358 million to over one billion by the turn of the century, making India the second country to pass the billion person milestone. While the rate of growth has slowed somewhat as India begins a demographics shift, the country’s population has continued to grow dramatically throughout the 21st century, and in 2020, India is estimated to have a population of just under 1.4 billion, well over a billion more people than one century previously. Today, approximately 18% of the Earth’s population lives in India, and it is estimated that India will overtake China to become the most populous country in the world within the next five years.

Japan Population Census: Age 80 to 84 Years data was reported at 4,961,420.000 Person in 2015. This records an increase from the previous number of 4,336,264.000 Person for 2010. Japan Population Census: Age 80 to 84 Years data is updated yearly, averaging 595,246.000 Person from Dec 1920 (Median) to 2015, with 20 observations. The data reached an all-time high of 4,961,420.000 Person in 2015 and a record low of 174,183.000 Person in 1920. Japan Population Census: Age 80 to 84 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.

Japan Population Census: Age 45 to 49 Years data was reported at 8,662,804.000 Person in 2015. This records an increase from the previous number of 8,033,116.000 Person for 2010. Japan Population Census: Age 45 to 49 Years data is updated yearly, averaging 5,439,514.500 Person from Dec 1920 (Median) to 2015, with 20 observations. The data reached an all-time high of 10,618,366.000 Person in 1995 and a record low of 2,658,567.000 Person in 1920. Japan Population Census: Age 45 to 49 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.