In Soviet Russia (RSFSR) in 1939 and 1959, ethnic Russians made up the largest share of the total population, with a share of approximately 83 percent. Tatars were the second largest ethnic group, followed by Ukrainians. Russians were consistently the largest ethnic group in the Soviet Union as a whole, with an overall share of 53 percent in 1979.

The Second World War had a profound impact on gender ratios within the Soviet Union's population, and its effect on different age groups varied greatly. The Soviet population structure had already been shaped heavily by the First World War, the Russian Revolution, and the famines of the early 1920s and early 1930s. The impact of these events on mortality and fertility meant that, in 1941, the generations whose births corresponded with these events had a lower population than would be expected on a typical population model. For example, in 1941, those aged between 5 and 9 had a significantly lower population than those aged 10 to 14, due to the effects of the Soviet famine of 1932-1933. Additionally, women outnumbered men in all age groups except the very youngest, due to the disproportionate effect of conflict and infant mortality on male populations. Impact of WWII In order to observe the impact of the war, one must compare populations of specific age groups in 1941 with the following age group in 1946. For men of "fighting age" in 1941, i.e. those aged between 15 and 44, these populations experience the most substantial decrease over the course of the war. For example, there are 5.6 million men aged 15-19 in 1941, but just 3.5 million aged 20-24 in 1946, giving a decrease of 38 percent. This decrease of almost forty percent can be observed until the 45-49 group, where the difference is 25 percent. Additionally, women aged between 15 and 34 saw a disproportionate decrease in their populations over this period, as many enlisted in the army and took an active part in the conflict, most notably as medics, snipers, and pilots.

The war's impact on fertility and child mortality meant that, in 1946, the total population under four years old was less than half its size in 1941. Generally, variations between age groups then fluctuated in line with pre-war patterns, however the overall ratio of women to men increased further after the war. For all age groups over 20 years, the number of men decreased between these years, whereas all women's age groups over 30 years saw an increase; this meant that, despite the war, women over 30 had a higher life expectancy in 1946.

This graph shows the total population of Estonia, Latvia and Lithuania in the years between 1922 and 1935, as well as the total number of males and females. After the First World War the Baltic states began claiming their independence from tsarist Russia, as the events of the Russian Revolution took place. Inter-war Estonia The Estonian War of Independence from 1918 to 1920 led to the country's first period of independence, until it became occupied by the Soviet Union again in 1940 during the Second World War. After Estonia gained independence the country experienced a period of political turmoil, including a failed coup d'etat in 1924, and was hit hard by the Great Depression in 1929 before things became more stable in the mid 1930s. Between 1939 and 1945 Estonia's population was devastated by the Second World War, with some estimates claiming that as many as 7.3 percent of all civilians perished as a result of the conflict. From the graph we can see the population grew by 119 thousand people during the 12 years shown, growing from 1.107 million to 1.126 million. The number of women was also higher than the number of men during this time, by 67 thousand in 1922 and 68 thousand in 1934. Inter-war Latvia For Latvia, Independence was a hard-won struggle that had devastated the population in the late 1910s. Similarly to Estonia, the advent of independence brought many challenges to Latvia, and a period of political and economic turmoil followed, which was exacerbated by the Great Depression in 1929. After economic recovery began in 1933, and a coup d'etat established stricter control in 1934, the Latvian economy and political landscape became more stable and the quality of life improved. This lasted until the Second World War, where Latvia became one of the staging grounds of Germany's war against Soviet Russia, and approximately 12.5 percent of all civilians died. From the data we can see that Latvia's population between 1925 and 1935 grew steadily by 95,000 in this decade, with the number of men and women growing at a similar rate. Inter-war Lithuania Lithuania's experience in the interwar period was slightly different to that of Latvia and Estonia. The end of the First World War led to a growing movement for independence from German, Russian or Polish influence, however these countries were reluctant to cede control to one another, and independence was finally achieved in 1922. A right wing dictatorship was established in 1926, which maintained political and civil control until the outbreak of the Second World War, however interference from other nations, particularly Germany, was ever-present in Lithuanian economic activity. From the graph we have only one set of figures, showing that the Lithuanian population was just over 2 million in 1929, with approximately 5 percent more women than men. World War II again devastated Lithuania's population, with almost 14.4 percent of the entire population falling during the conflict.

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.

The world's Jewish population has had a complex and tumultuous history over the past millennia, regularly dealing with persecution, pogroms, and even genocide. The legacy of expulsion and persecution of Jews, including bans on land ownership, meant that Jewish communities disproportionately lived in urban areas, working as artisans or traders, and often lived in their own settlements separate to the rest of the urban population. This separation contributed to the impression that events such as pandemics, famines, or economic shocks did not affect Jews as much as other populations, and such factors came to form the basis of the mistrust and stereotypes of wealth (characterized as greed) that have made up anti-Semitic rhetoric for centuries. Development since the Middle Ages The concentration of Jewish populations across the world has shifted across different centuries. In the Middle Ages, the largest Jewish populations were found in Palestine and the wider Levant region, with other sizeable populations in present-day France, Italy, and Spain. Later, however, the Jewish disapora became increasingly concentrated in Eastern Europe after waves of pogroms in the west saw Jewish communities move eastward. Poland in particular was often considered a refuge for Jews from the late-Middle Ages until the 18th century, when it was then partitioned between Austria, Prussia, and Russia, and persecution increased. Push factors such as major pogroms in the Russian Empire in the 19th century and growing oppression in the west during the interwar period then saw many Jews migrate to the United States in search of opportunity.

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.

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.

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.

In 1750, when Finland was part of the Duchy of Sweden, and had a total population of just 422 thousand. Over the next 55 years the population grows steadily and reaches 896 thousand people, before it drops to 863 thousand in 1810. The Finnish borders did expand during the early 1800s, adding 12,000 people in 1809 and 185 thousand in 1811, however the dip in the graph most probably occurs as a result of the Finnish War, fought between Sweden and Russia in 1808 and 1809, and this war resulted in Finland becoming a part of the Russian Empire. From 1810 to 1865 the population then grows steadily again, until 1870 when it dips again from 1.84 million to 1.77 million. This second dip in population size is due to the Finnish famine of 1866-68, which resulted in the fatalities of around 8.5% of the entire Finnish population.

Throughout the twentieth century and until now the population has grown with each entry in the graph. Finland gained independence in 1918 after a brief civil war, and it was also heavily involved in fighting against Russia in World War II, and between 85 and 90 thousand people (2.3 to 2.6 percent of the total population) are estimated to have died as a direct result of the war. In spite of this the population has grown at a consistent rate (although the graph appears skewed as the intervals change from 10 years to 5 years in 1950), and the total population is expected to reach 5.5 million in 2020

In 1844, Romania had a population of just 3.6 million people. During the early entries in this data, Romania's borders were very different and much smaller than today, and control of this area often switched hands between the Austrian, Ottoman and Russian empires. The populations during this time are based on estimates made for incomplete census data, and they show that the population grows from 3.6 million in 1844, doubling to 7.2 million in 1912, part of this growth is due to a high natural birth rate during this period, but also partly due to the changing of Romania's borders and annexation of new lands. During this time Romania gained its independence from the Ottoman Empire as a result of the Russo-Turkish War in 1878, and experienced a period of increased stability and progress.

Between 1912 and 1930 the population of Romania grew by over 10 million people. The main reason for this is the huge territories gained by Romania in the aftermath of the First World War. During the war Romania remained neutral for the first two years, after which it joined the allies; however, it was very quickly defeated and overrun by the Central Powers, and in total it lost over 600 thousand people as a direct result of the war. With the collapse of the Austro-Hungarian and Russian empires after the war, Romania gained almost double it's territory, which caused the population to soar to 18.1 million in 1930. The population then decreases by 1941 and again by 1948, as Romania seceded territory to neighboring countries and lost approximately half a million people during the Second World War. From 1948 onwards the population begins to grow again, reaching it's peak at 23.5 million people in 1990.

Like many other Eastern European countries, there was very limited freedom of movement from Romania during the Cold War, and communist rule was difficult for the Romanian people. The Romanian Revolution in 1989 ended communist rule in the country, Romania transitioned to a free-market society and movement from the country was allowed. Since then the population has fallen each year as more and more Romanians move abroad in search of work and opportunities. The population is expected to fall to 19.2 million in 2020, which is over 4 million fewer people than it had in 1990.