From the mid-19th century until today, life expectancy at birth in the United States has roughly doubled, from 39.4 years in 1850 to 79.6 years in 2025. It is estimated that life expectancy in the U.S. began its upward trajectory in the 1880s, largely driven by the decline in infant and child mortality through factors such as vaccination programs, antibiotics, and other healthcare advancements. Improved food security and access to clean water, as well as general increases in living standards (such as better housing, education, and increased safety) also contributed to a rise in life expectancy across all age brackets. There were notable dips in life expectancy; with an eight year drop during the American Civil War in the 1860s, a seven year drop during the Spanish Flu empidemic in 1918, and a 2.5 year drop during the Covid-19 pandemic. There were also notable plateaus (and minor decreases) not due to major historical events, such as that of the 2010s, which has been attributed to a combination of factors such as unhealthy lifestyles, poor access to healthcare, poverty, and increased suicide rates, among others. However, despite the rate of progress slowing since the 1950s, most decades do see a general increase in the long term, and current UN projections predict that life expectancy at birth in the U.S. will increase by another nine years before the end of the century.

For most of the world, throughout most of human history, the average life expectancy from birth was around 24. This figure fluctuated greatly depending on the time or region, and was higher than 24 in most individual years, but factors such as pandemics, famines, and conflicts caused regular spikes in mortality and reduced life expectancy. Child mortality The most significant difference between historical mortality rates and modern figures is that child and infant mortality was so high in pre-industrial times; before the introduction of vaccination, water treatment, and other medical knowledge or technologies, women would have around seven children throughout their lifetime, but around half of these would not make it to adulthood. Accurate, historical figures for infant mortality are difficult to ascertain, as it was so prevalent, it took place in the home, and was rarely recorded in censuses; however, figures from this source suggest that the rate was around 300 deaths per 1,000 live births in some years, meaning that almost one in three infants did not make it to their first birthday in certain periods. For those who survived to adolescence, they could expect to live into their forties or fifties on average. Modern figures It was not until the eradication of plague and improvements in housing and infrastructure in recent centuries where life expectancy began to rise in some parts of Europe, before industrialization and medical advances led to the onset of the demographic transition across the world. Today, global life expectancy from birth is roughly three times higher than in pre-industrial times, at almost 73 years. It is higher still in more demographically and economically developed countries; life expectancy is over 82 years in the three European countries shown, and over 84 in Japan. For the least developed countries, mostly found in Sub-Saharan Africa, life expectancy from birth can be as low as 53 years.

The child mortality rate in the United States, for children under the age of five, was 462.9 deaths per thousand births in 1800. This means that for every thousand babies born in 1800, over 46 percent did not make it to their fifth birthday. Over the course of the next 220 years, this number has dropped drastically, and the rate has dropped to its lowest point ever in 2020 where it is just seven deaths per thousand births. Although the child mortality rate has decreased greatly over this 220 year period, there were two occasions where it increased; in the 1870s, as a result of the fourth cholera pandemic, smallpox outbreaks, and yellow fever, and in the late 1910s, due to the Spanish Flu pandemic.

The child mortality rate in China, for children under the age of five, was 417 deaths per thousand births in 1850. This means that for all children born in 1850, almost 42 percent did not make it to their fifth birthday. Over the course of the next 170 years, this number has dropped drastically, and the rate has dropped to its lowest point ever in 2020 where it is just twelve deaths per thousand births. The sharpest decrease came between 1950 and 1955, as the Chinese Civil War ended, and the country began to recover from the Second World War. The decline then stopped between 1955 and 1965, due to famines caused by Chairman Mao Zedong's attempted Great Leap Forward, which was a failed attempt to industrialize China in the late twentieth century.

The child mortality rate in the United Kingdom, for children under the age of five, was 329 deaths per thousand births in 1800. This means that approximately one in every three children born in 1800 did not make it to their fifth birthday. Over the course of the next 220 years, this number has dropped drastically, particularly in the first half of the twentieth century, and the rate has dropped to its lowest point ever in 2020 where it is just four deaths per thousand births.

The child mortality rate in Canada, for children under the age of five, was 333 deaths per thousand births in the year 1830. This means that one third of all children born in 1830 did not make it to their fifth birthday. Child mortality remained above 25 percent for the remainder of the nineteenth century, before falling at a much faster rate throughout the 1900s. By the year 2020, Canada's child mortality rate is expected to be just five deaths per thousand births.

The child mortality rate in Australia, for children under the age of five, was 391 deaths per thousand births in 1860. This means that just under forty percent of all children born in 1860 did not make it to their fifth birthday. This number dropped drastically over the next ten years, then it remained between 150 and two hundred for the remainder of the 1800s, before dropping consistently from 1900 until today. By 2020, child mortality in Australia is expected to be approximately four deaths per thousand births.

In 1800, the population of the area of modern-day Pakistan was estimated to be just over 13 million. Population growth in the 19th century would be gradual in the region, rising to just 19 million at the turn of the century. In the early 1800s, the British Empire slowly consolidated power in the region, eventually controlling the region of Pakistan from the mid-19th century onwards, as part of the British Raj. From the 1930s on, the population's growth rate would increase as improvements in healthcare (particularly vaccination) and sanitation would lead to lower infant mortality rates and higher life expectancy. Independence In 1947, the Muslim-majority country of Pakistan gained independence from Britain, and split from the Hindu-majority country of India. In the next few years, upwards of ten million people migrated between the two nations, during a period that was blemished by widespread atrocities on both sides. Throughout this time, the region of Bangladesh was also a part Pakistan (as it also had a Muslim majority), known as East Pakistan; internal disputes between the two regions were persistent for over two decades, until 1971, when a short but bloody civil war resulted in Bangladesh's independence. Political disputes between Pakistan and India also created tension in the first few decades of independence, even boiling over into some relatively small-scale conflicts, although there was some economic progress and improvements in quality of life for Pakistan's citizens. The late 20th century was also characterized by several attempts to become democratic, but with intermittent periods of military rule. Between independence and the end of the century, Pakistan's population had grown more than four times in total. Pakistan today Since 2008, Pakistan has been a functioning democracy, with an emerging economy and increasing international prominence. Despite the emergence of a successful middle-class, this is prosperity is not reflected in all areas of the population as almost a quarter still live in poverty, and Pakistan ranks in the bottom 20% of countries according to the Human Development Index. In 2020, Pakistan is thought to have a total population of over 220 million people, making it the fifth-most populous country in the world.

In 1800, the region of present-day Turkey had a population of approximately 9.8 million. Turkey’s population would grow steadily throughout the 1800s, growing to 14 million by the turn of the century. During this time, Turkey was the center of the Ottoman Empire, which also covered much of the Balkans, Arabia, and the African coast from Libya to Somalia. In the early 20th century, the Ottoman Empire's dissolution period began, characterized by political instability and a series of military defeats and coups. The empire was one of the defeated Central Powers of the First World War, in which it suffered approximately three million total fatalities. It is estimated that the majority of these deaths did not come directly from the war, but as a result of the government-orchestrated mass expulsion and genocide of non-Turks from within the Turkish borders, specifically Armenians, Assyrians, Greeks and Kurds; many ethnic Turks were simultaneously expelled from neighboring countries, namely Greece, which makes these events less-visible when examining annual data, although Turkey's total population did drop by one million between 1914 and 1924.

The Republic of Turkey Following the end of the Turkish War of Independence in 1923, and the establishment of the republic of Turkey, the population would begin to recover, tripling from just around 21 million in 1950 to over 63 million by the turn of the century. The new republic, led by Mustafa Kemal Atatürk, introduced sweeping, progressive reforms that modernized the country, particularly its healthcare and education systems. Turkey remained neutral throughout the Second World War, and became a member of NATO during the Cold War. The second half of the 1900s was marked with intermittent periods of political instability, and a number of military conflicts (namely, in Cyprus and Kurdistan). In spite of this, Turkey has generally been considered a developed country for most of this time, although its life expectancy and infant mortality rates have often been more in line with developing nations.

Modern Turkey In the past decade, Turkey's population growth has continued its rapid growth; while birth rates have declined, the mass migration of refugees to the country fleeing the Syrian Civil War has seen the population growth ramain high. This influx of refugees was seen as a stepping stone in Turkey's accession to the European Union, with whom it has been negotiating a potential membership since 2005. Accession to the EU would provide huge economic benefits to Turkey, however, political developments in recent years (particularly the 2016 coup) have seen these negotiations stall, as the EU has accused the Turkish government of committing widespread human rights violations, such as torture, political imprisonment and censorship of free speech. In 2020, Turkey's population is estimated to be over 84 million people, and is expected to exceed 100 million in the next two decades.