The earliest point where scientists can make reasonable estimates for the population of global regions is around 10,000 years before the Common Era (or 12,000 years ago). Estimates suggest that Asia has consistently been the most populated continent, and the least populated continent has generally been Oceania (although it was more heavily populated than areas such as North America in very early years). Population growth was very slow, but an increase can be observed between most of the given time periods. There were, however, dips in population due to pandemics, the most notable of these being the impact of plague in Eurasia in the 14th century, and the impact of European contact with the indigenous populations of the Americas after 1492, where it took almost four centuries for the population of Latin America to return to its pre-1500 level. The world's population first reached one billion people in 1803, which also coincided with a spike in population growth, due to the onset of the demographic transition. This wave of growth first spread across the most industrially developed countries in the 19th century, and the correlation between demographic development and industrial or economic maturity continued until today, with Africa being the final major region to begin its transition in the late-1900s.

Prior to the arrival of European explorers in the Americas in 1492, it is estimated that the population of the continent was around sixty million people. Over the next two centuries, most scholars agree that the indigenous population fell to just ten percent of its pre-colonization level, primarily due to the Old World diseases (namely smallpox) brought to the New World by Europeans and African slaves, as well as through violence and famine.

Distribution

It is thought that the most densely populated region of the Americas was in the fertile Mexican valley, home to over one third of the entire continent, including several Mesoamerican civilizations such as the Aztec empire. While the mid-estimate shows a population of over 21 million before European arrival, one estimate suggests that there were just 730,000 people of indigenous descent in Mexico in 1620, just one hundred years after Cortes' arrival. Estimates also suggest that the Andes, home to the Incas, was the second most-populous region in the Americas, while North America (in this case, the region north of the Rio Grande river) may have been the most sparsely populated region. There is some contention as to the size of the pre-Columbian populations in the Caribbean, as the mass genocides, forced relocation, and pandemics that followed in the early stages of Spanish colonization make it difficult to predict these numbers.

Varying estimates Estimating the indigenous populations of the Americas has proven to be a challenge and point of contention for modern historians. Totals from reputable sources range from 8.4 million people to 112.55 million, and while both of these totals were published in the 1930s and 1960s respectively, their continued citation proves the ambiguity surrounding this topic. European settlers' records from the 15th to 17th centuries have also created challenges, due to their unrealistic population predictions and inaccurate methodologies (for example, many early settlers only counted the number of warriors in each civilization). Nonetheless, most modern historians use figures close to those given in the "Middle estimate" shown here, with similar distributions by region.

In 1500, the largest city was Paris, with an estimated 225 thousand inhabitants, almost double the population of the second-largest city, Naples. As in 1330, Venice and Milan remain the third and fourth largest cities in Western Europe, however Genoa's population almost halved from 1330 until 1500, as it was struck heavily by the bubonic plague in the mid-1300s. In lists prior to this, the largest cities were generally in Spain and Italy, however, as time progressed, the largest populations could be found more often in Italy and France. The year 1500 is around the beginning of what we now consider modern history, a time that saw the birth of many European empires and inter-continental globalization.

Prior to 1829, the area of modern day Greece was largely under the control of the Ottoman Empire. In 1821, the Greeks declared their independence from the Ottomans, and achieved it within 8 years through the Greek War of Independence. The Independent Kingdom of Greece was established in 1829 and made up the southern half of present-day, mainland Greece, along with some Mediterranean islands. Over the next century, Greece's borders would expand and readjust drastically, through a number of conflicts and diplomatic agreements; therefore the population of Greece within those political borders** was much lower than the population in what would be today's borders. As there were large communities of ethnic Greeks living in neighboring countries during this time, particularly in Turkey, and the data presented here does not show the full extent of the First World War, Spanish Flu Pandemic and Greko-Turkish War on these Greek populations. While it is difficult to separate the fatalities from each of these events, it is estimated that between 500,000 and 900,000 ethnic Greeks died at the hands of the Ottomans between the years 1914 and 1923, and approximately 150,000 died due to the 1918 flu pandemic. These years also saw the exchange of up to one million Orthodox Christians from Turkey to Greece, and several hundred thousand Muslims from Greece to Turkey; this exchange is one reason why Greece's total population did not change drastically, despite the genocide, displacement and demographic upheaval of the 1910s and 1920s. Greece in WWII A new Hellenic Republic was established in 1924, which saw a decade of peace and modernization in Greece, however this was short lived. The Greek monarchy was reintroduced in 1935, and the prime minister, Ioannis Metaxas, headed a totalitarian government that remained in place until the Second World War. Metaxas tried to maintain Greek neutrality as the war began, however Italy's invasion of the Balkans made this impossible, and the Italian army tried invading Greece via Albania in 1940. The outnumbered and lesser-equipped Greek forces were able to hold off the Italian invasion and then push them backwards into Albania, marking the first Allied victory in the war. Following a series of Italian failures, Greece was eventually overrun when Hitler launched a German and Bulgarian invasion in April 1941, taking Athens within three weeks. Germany's involvement in Greece meant that Hitler's planned invasion of the Soviet Union was delayed, and Hitler cited this as the reason for it's failure (although most historians disagree with this). Over the course of the war approximately eight to eleven percent of the Greek population died due to fighting, extermination, starvation and disease; including over eighty percent of Greece's Jewish population in the Holocaust. Following the liberation of Greece in 1944, the country was then plunged into a civil war (the first major conflict of the Cold War), which lasted until 1949, and saw the British and American-supported government fight with Greek communists for control of the country. The government eventually defeated the Soviet-supported communist forces, and established American influence in the Aegean and Balkans throughout the Cold War. Post-war Greece From the 1950s until the 1970s, the Marshall Plan, industrialization and an emerging Tourism sector helped the Greek economy to boom, with one of the strongest growth rates in the world. Apart from the military coup, which ruled from 1967 to 1974, Greece remained relatively peaceful, prosperous and stable throughout the second half of the twentieth century. The population reached 11.2 million in the early 2000s, before going into decline for the past fifteen years. This decline came about due to a negative net migration rate and slowing birth rate, ultimately facilitated by the global financial crisis of 2007 and 2008; many Greeks left the country in search of work elsewhere, and the economic troubles have impacted the financial incentives that were previously available for families with many children. While the financial crisis was a global event, Greece was arguably the hardest-hit nation during the crisis, and suffered the longest recession of any advanced economy. The financial crisis has had a consequential impact on the Greek population, which has dropped by 800,000 in 15 years, and the average age has increased significantly, as thousands of young people migrate in search of employment.

Albania, then known as Rumelia, was a province of the Ottoman Empire from the fifteenth century until it declared it's independence in 1912. Following a series of unsuccessful uprisings and brief occupations from nearby Serbia and Greece, Albania finally claimed its independence on November 28, 1912; however the Conference of London in 1913 then set the borders of the former-Ottoman states in Southern Europe, which left many ethnic Albanians living in other neighboring states, particularly Serbia (and what is now Kosovo). The newly-formed Albanian state collapsed in the wake of the First World War, and was controlled in parts by Greece, Italy and Serbia. The Paris Conference then established an independent Albanian state, which led to a period of political and economic turmoil that lasted until Italy's annexation of the region in 1939, during the Second World War. It is estimated that just under 3 percent of Albania's population perished as a direct result of the war, as Albania became the main theater for the Axis Powers' war against Greece. Italy then surrendered control of the area to Germany in 1943, and after the war ended in 1945, Albania became a Yugoslav satellite state and remained behind the Iron Curtain until it's collapse in the 1990s. Steady growth during the communist era From the war's end onwards, Albania's population enjoyed steady growth and almost tripled by 1990. Throughout this time, Albania underwent a series of political allegiances; first as a Yugoslav and then Soviet satellite states, but then became an important actor in the Sino-Soviet split, eventually siding with China in the 1960s. Gradually, Albania transitioned into a more isolationist and independent country in in the 1970s, and slowly adopted some more democratic practices. The total population surpassed two million people in the late 1960s, and three million in the late 1980s, but then a dramatic change in population growth occurred in the 1990s, as communism in Europe came to an end. Immediate decline following communism's end Increased freedom of movement, improved access to contraception and major lifestyle changes caused the population to fall into decline. The population did increase in the late 90s, despite a civil war in the first half of 1997 (in which over 2 thousand people died) sparked by a failure of the financial system in Albania. The Albanian Army was also involved in the war in neighboring Kosovo between 1998 and 1999. The 2000s brought about further decline, and the population is just 2.9 million in 2020, a decline of approximately 400,000 people in thirty years. Albania has been a candidate for accession to the EU since 2014, and membership would bring further change to the country.

It is estimated that the cities of Cordova (modern-day Córdoba) and Palermo were the largest cities in Europe in 1050, and had between fifteen and twenty times the population of most other entries in this graph, Despite this the cities of Cordova (the capital city of the Umayyad caliphate, who controlled much of the Iberian peninsula from the seventh to eleventh centuries), and Palermo (another Arab-controlled capital in Southern Europe) were still the only cities in Western Europe with a population over one hundred thousand people, closely followed by Seville. It is also noteworthy to point out that the five largest cities on this list were importing trading cities, in modern day Spain or Italy, although the largest cities become more northern and western European in later lists (1200, 1330, 1500, 1650 and 1800). In 1050, todays largest Western European cities, London and Paris, had just twenty-five and twenty thousand inhabitants respectively.

The period of European history (and much of world history) between 500 and 1500 is today known as the 'Dark Ages'. Although the term 'Dark Ages' was originally applied to the lack of literature and arts, it has since been applied to the lack or scarcity of recorded information from this time. Because of these limitations, much information about this time is still being debated today.

Sikhism is a religion that originated on the Indian subcontinent during the fifteenth century. Sikhs follow the teachings of 'gurus', who descend from the first guru Guru Naruk who established the faith. Followers of Sikhism are monotheists, believing in only one god, and other core beliefs include the need to meditate, the importance of community and communal living, and the need to serve humanity selflessly (or 'seva'). Sikhism and the British Empire In total, there are around 26 million Sikhs worldwide, and over 24 million of these live in India. Outside of India, the largest Sikh populations are mostly found in former territories of the British Empire - the UK and Canada both have Sikh populations of over half a million people. Migration from India to other parts of the British Empire was high in the 19th century, due to the labor demands of relatively newer colonies, as well as those where slavery had been abolished. These countries also remain popular destinations for Sikh migrants today, as many are highly trained and English-speaking. Other regions with significant Sikh populations Italy also has a sizeable Sikh population, as many migrated there after serving there in the British Army during WWI, and they are now heavily represented in Italy's dairy industry. The Sikh population of Saudi Arabia is also reflective of the fact that the largest Indian diaspora in the world can now be found in the Middle East - this is due to the labor demands of the fossil fuel industries and their associated secondary industries, although a large share of Indians in this part of the world are there on a temporary basis.

In the nineteenth and twentieth centuries, the majority of documented migration to the United States of American came from European countries. Between 1820 and 1957, of the approximate 41 million migrants to the US, over 34 million of these came from Europe. The most commonly documented countries of origin during this time were Germany (6.6 million), Italy (4.9 million), Ireland (4.6 million), Great Britain (4.5 million), and Russia (3.4 million). The first wave of mass migration came in the 1850s, as the Great famine crippled Ireland's population, and many in rural areas of mainland Europe struggled to adapt to industrialization, and economic opportunities attracted many in the 1870s, following the American Civil War. The 1880s saw another wave, as steam powered ships and lower fares made trans-Atlantic journeys much more affordable. The first wave of mass migration from Eastern and Southern Europe also arrived at this time, as industrialization and agricultural advancements led to high unemployment in these regions.

The majority of migrants to the United States settled in major urban centers, which allowed the expansion of industry, leading to the United States' emergence as one of the leading global economies at the turn of the twentieth century. The largest wave of migration to the United states during this period came in the first fifteen years of the 1900s. The influx of migrants from Northern and Western Europe had now been replaced by an influx from Eastern and Southern Europe (although migration from the British Isles was still quite high during this time). European migration fell to it's lowest levels in eighty years during the First World War, before fluctuating again in the interwar period, due to the Great Depression. As the twentieth century progressed, the continent with the highest levels of migration to the US gradually changed from Europe to Latin America, as economic opportunities in Western Europe improved, and the US' relationship with the Soviet Union and other Eastern, communist states became complicated.