Over the past 160 years, life expectancy (from birth) in the United States has risen from 39.4 years in 1860, to 78.9 years in 2020. One of the major reasons for the overall increase of life expectancy in the last two centuries is the fact that the infant and child mortality rates have decreased by so much during this time. Medical advancements, fewer wars and improved living standards also mean that people are living longer than they did in previous centuries.

Despite this overall increase, the life expectancy dropped three times since 1860; from 1865 to 1870 during the American Civil War, from 1915 to 1920 during the First World War and following Spanish Flu epidemic, and it has dropped again between 2015 and now. The reason for the most recent drop in life expectancy is not a result of any specific event, but has been attributed to negative societal trends, such as unbalanced diets and sedentary lifestyles, high medical costs, and increasing rates of suicide and drug use.

A global phenomenon, known as the demographic transition, has seen life expectancy from birth increase rapidly over the past two centuries. In pre-industrial societies, the average life expectancy was around 24 years, and it is believed that this was the case throughout most of history, and in all regions. The demographic transition then began in the industrial societies of Europe, North America, and the West Pacific around the turn of the 19th century, and life expectancy rose accordingly. Latin America was the next region to follow, before Africa and most Asian populations saw their life expectancy rise throughout the 20th century.

Life expectancy in Spain was below thirty in the year 1880, and over the course of the next 140 years, it is expected to have increased to 83.4 by the year 2020. Although life expectancy has generally increased throughout Spain's history, there were several times where the rate deviated from its previous trajectory. The most notable changes were a result of the global influenza epidemic of the 1910s, (called the 'Spanish Flu' as it received more press coverage in neutral Spain, during the First World War) and the Spanish Civil War two decades later.

In 1880, the average person born in the area of modern day Yemen could expect to live to just over the age of 23, a rate which would remain largely unchanged throughout the end of the 19th and first half of the 20th century (outside of a small dip from the Spanish Flu in the late 1910s). However, life expectancy in Yemen would begin to rise greatly in the 1950s, as Imam Ahmed would open up the country from its isolationist policies, allowing for a significant expansion in economic growth and improvements to healthcare and living standards. Yemen’s growing oil revenues fueled these developments, resulting in life expectancy more than doubling by the end of the century. However, life expectancy would slow and ultimately stagnate in the 21th century, as the Yemeni Civil War would continue to cause significant disruptions in healthcare services and severe famine in the country. As a result, it is estimated in 2020 that the average person born in Yemen can expect to live to just over the age of 66 years old.

Life expectancy in Germany was below 39 in the year 1875, and over the course of the next 145 years, it is expected to have increased to above 81 years in the year 2020. Although life expectancy has generally increased throughout Germany's history, there were several times where the rate deviated from its previous trajectory. The most notable changes were because of the First and Second World Wars, in the first half of the twentieth century.

In 1880, the average person born in the area of modern-day South Korea could expect to live to just under the age of 26, a figure which would remain below thirty until the 1920s. Life expectancy would fall to its lowest level of just 24 years in 1920, however, as the 1918 Spanish Flu epidemic would spread through the country, resulting in an estimated 200,000 deaths across the Korean peninsula. Life expectancy would begin to rise in the 1920s, however, as development programs by the Japanese colonial administration would see economic growth and access to healthcare improve greatly in the region. The 1940s and 1950s would see a slowing, then a reversal to this growth though, as the final years of the Second World War, and later the 1950 Korean War, would see significant destruction and fatalities in the country.

Following the end of the Korean War with the 1953 armistice, life expectancy would begin to climb again in the newly-established South Korea, as the country would begin to rapidly modernize and improve access to healthcare and nutrition, raising standards of living and cutting child mortality rates throughout the country. As a result, life expectancy would rise from just under 47 years in 1950, to over 75 years by the turn of the century. This rise in life expectancy has continued steadily into the 21st century, and as a result, in 2020, it is estimated that the average person born in South Korea will live to just under the age of 83 years, one of the highest life expectancies in the world.

Life expectancy in the United Kingdom was below 39 years in the year 1765, and over the course of the next two and a half centuries, it is expected to have increased by more than double, to 81.1 by the year 2020. Although life expectancy has generally increased throughout the UK's history, there were several times where the rate deviated from its previous trajectory. These changes were the result of smallpox epidemics in the late eighteenth and early nineteenth centuries, new sanitary and medical advancements throughout time (such as compulsory vaccination), and the First world War and Spanish Flu epidemic in the 1910s.

Life expectancy in China was just 32 in the year 1850, and over the course of the next 170 years, it is expected to more than double to 76.6 years in 2020. Between 1850 and 1950, finding reliable data proved difficult for anthropologists, however some events, such as the Taiping Rebellion and Dungan Revolt in the nineteenth century did reduce life expectancy by a few years, and also the Chinese Civil War and Second World War in the first half of the twentieth century. In the second half of the 1900s, Chinese life expectancy increased greatly, as the country became more industrialized and the standard of living increased.

At the beginning of the 1840s, life expectancy from birth in Ireland was just over 38 years. However, this figure would see a dramatic decline with the beginning of the Great Famine in 1845, and dropped below 21 years in the second half of the decade (in 1849 alone, life expectancy fell to just 14 years). The famine came as a result of a Europe-wide potato blight, which had a disproportionally devastating impact on the Irish population due to the dependency on potatoes (particularly in the south and east), and the prevalence of a single variety of potato on the island that allowed the blight to spread faster than in other areas of Europe. Additionally, authorities forcefully redirected much of the country's surplus grain to the British mainland, which exacerbated the situation. Within five years, mass starvation would contribute to the deaths of over one million people on the island, while a further one million would emigrate; this also created a legacy of emigration from Ireland, which saw the population continue to fall until the mid-1900s, and the total population of the island is still well below its pre-famine level of 8.5 million people.

Following the end of the Great Famine, life expectancy would begin to gradually increase in Ireland, as post-famine reforms would see improvements in the living standards of the country’s peasantry, most notably the Land Wars, a largely successful series of strikes, boycotts and protests aimed at reform of the country's agricultural land distribution, which began in the 1870s and lasted into the 20th century. As these reforms were implemented, life expectancy in Ireland would rise to more than fifty years by the turn of the century. While this rise would slow somewhat in the 1910s, due to the large number of Irish soldiers who fought in the First World War and the Spanish Flu pandemic, as well as the period of civil unrest leading up to the island's partition in 1921, life expectancy in Ireland would rise greatly in the 20th century. In the second half of the 20th century, Ireland's healthcare system and living standards developed similarly to the rest of Western Europe, and today, it is often ranks among the top countries globally in terms of human development, GDP and quality of healthcare. With these developments, the increase in life expectancy from birth in Ireland was relatively constant in the first century of independence, and in 2020 is estimated to be 82 years.

Life expectancy in Italy was just under thirty in the year 1870, and over the course of the next 150 years, it is expected to have increased to 83.3 by the year 2020. Although life expectancy has generally increased throughout Italy's history, there were several times where the rate deviated from its previous trajectory. The most noticeable changes were a result of the First World War and Spanish Flu epidemic, and also the Second World War and Italian Civil War.

Life expectancy in India was 25.4 in the year 1800, and over the course of the next 220 years, it has increased to almost 70. Between 1800 and 1920, life expectancy in India remained in the mid to low twenties, with the largest declines coming in the 1870s and 1910s; this was because of the Great Famine of 1876-1878, and the Spanish Flu Pandemic of 1918-1919, both of which were responsible for the deaths of up to six and seventeen million Indians respectively; as well as the presence of other endemic diseases in the region, such as smallpox. From 1920 onwards, India's life expectancy has consistently increased, but it is still below the global average.

Life expectancy in Japan was 36.4 in the year 1860, and over the course of the next 160 years, it is expected to have increased to 84.4, which is the second highest in the world (after Monaco). Although life expectancy has generally increased throughout Japan's history, there were several times where the rate deviated from its previous trajectory. These changes were a result of the Spanish Flu in the 1910s, the Second World War in the 1940s, and the sharp increase was due to the high rate of industrialization and economic prosperity in Japan, in the mid-twentieth century.

Life expectancy in Canada was just below forty in the year 1800, and over the course of the next 220 years, it is expected to have increased by more than double to 82.2 by the year 2020. Throughout this time, life expectancy in Canada progressed at a steady rate, with the most noticeable changes coming during the interwar period, where the rate of increase was affected by the Spanish Flu epidemic and both World Wars.

Life expectancy in Russia was 29.6 in the year 1845, and over the course of the next 175 years, it is expected to have increased to 72.3 years by 2020. Generally speaking, Russian life expectancy has increased over this 175 year period, however events such as the World Wars, Russian Revolution and a series of famines caused fluctuations before the mid-twentieth century, where the rate fluctuated sporadically. Between 1945 and 1950, Russian life expectancy more than doubled in this five year period, and it then proceeded to increase until the 1970s, when it then began to fall again. Between 1970 and 2005, the number fell from 68.5 to 65, before it then grew again in more recent years.

Life expectancy in France was below thirty in the late 1700s, but over the course of the next two and a half centuries it is expected to reach 82.5 by the year 2020. Although life expectancy has generally increased throughout France's history, there were several times where the rate deviated from its previous trajectory. The most noticeable changes were because of smallpox and influenza epidemics in the 1700s, medical advancements (such as vaccination and pasteurization) saw life expectancy increase in the 1800s, and then both World Wars and the epidemics that followed caused brief drops in the first half of the twentieth century.

Life expectancy in Sweden was 36 in the year 1765, and over the course of the next 255 years, it is expected to have increased to 82.6 by 2020. Although life expectancy has generally increased throughout Sweden's history, there was a lot of fluctuation around the turn of the nineteenth century due to The Napoleonic Wars and First Cholera Epidemic, and again in the 1910s due to the Spanish Flu Epidemic.

Life expectancy in Australia was just below 35 in the year 1870, and over the course of the next 150 years, it is expected to have increased to 83.2 by the year 2020. Although life expectancy has generally increased throughout Australia's history, there were several times where the rate deviated from its previous trajectory. the most noticeable changes were between 1890 and 1920. This period included Australia's Independence movement, the implementation of the 'White Australia' policy, the First World War and Spanish Flu epidemic, all of which impacted the demographics of Australia.

Life expectancy in Iceland was just over forty in the year 1765, and over the course of the next 255 years, it is expected to have increased to 82.8 by the year 2020. Although life expectancy has generally increased throughout Iceland's history, there was a lot of fluctuation in the data before the twentieth century, and life expectancy was rarely above forty years. However, from 1885 onwards, Iceland's life expectancy has generally increased, and is expected to be one of the highest in the world in 2020.

In 1870, the average person born in the Democratic Republic of the Congo (DRC) could expect to live 31.6 years on average. Under Belgian colonial rule, life expectancy would grow steadily into the 20th century, with a temporary drop in 1920 as the 1918 Spanish Flu epidemic would spread rapidly through the country’s extensive river basin. Beginning in the 1940s and 1950s, life expectancy in the DRC would begin to rise greatly, as the Belgian colonial administration aimed to make the country into a “model colony”. However, after peaking at 41.2 years in 1950, increasing instability in the country would see life expectancy to fall to 39 years by 1955.

Life expectancy would begin to grow again in the 1960s, however, and would rise steadily until the turn of the century, when an escalation in the Second Congo War and the growing presence of the HIV/AIDS epidemic in the country would cause life expectancy to fall for the first time in almost half a century. With the end of the Second Congo War in 2003, and significantly improvements in access to HIV counselling and treatments in the region, life expectancy in the DRC would begin to rise again, and in 2020, it is estimated that the average person born in the DRC will live to just over the age of 60.

Life expectancy in New Zealand was just over 34 in the year 1870, and over the course of the next 150 years, it is expected to have increased to just over 82 by the year 2020. Although life expectancy has generally increased along a gradual curve throughout New Zealand's history, there was a slight dip in the late 1910s, as a result of the First World War and following influenza epidemic. Apart from this, there were no anomalies that reduced life expectancy throughout this 150 year period.