In 1800, it is estimated that approximately 4.35 million people lived in the region of present-day North Korea. This figure would remain stagnant through much of the 19th century, increasing by just one million people over the next 110 years. The dissolution of the Joseon dynasty in the Korean peninsula in the late-1800s marked the end of centuries of Korean isolationism, and the new Korean Empire then opened itself to foreign trade and influence. By the start of the 20th century, the region of North Korea had a population of just over five million. This growth would increase dramatically following the annexation of the Korean peninsula by Japan in 1910, as extensive industrialization and modernization efforts would result in the population of North Korea doubling from just over five million at the turn of the century, to over ten and a half million by the start of the Korean War in 1950. The Korean War Following Japan's defeat in the Second World War, the Korean Peninsula was split along the 38th parallel, with a Soviet-backed totalitarian government established in the north, and a U.S.-backed authoritarian government in the south. Neither government recognized the legitimacy of the other, and an escalation of tensions saw the North invade the South in June 1950. By 1953, the North's population dropped below ten million. It is estimated that there were approximately three million total fatalities in the war, with North Korea having the largest share of fatalities of all forces involved; however, the North's isolationist and secretive policies have made it difficult to calculate the full impact of the war on the North's population. Most modern estimates suggest that more than 1.5 million North Koreans died or went missing over these three years. Following the establishment of an armistice between North and South Korea in 1953, the population of the newly-formed Democratic People's Republic of North Korea would begin to rise sharply, from 10 million at the time of armistice to almost 15 million in 1970, just twenty years later. North Korea today North Korea's population has increased in each year since the war's end, however, the rate of growth decreased in the late 1970s, as a severe economic crisis and a resulting lack of foreign technology would lead to a scaling back of many of social welfare programs for the country’s citizens. Growth would slow even further following the dissolution of the Soviet Union in 1991, as the loss of Soviet foreign aid would send the North Korean economy into a sharp decline. In the 1990s, a series of flooding, droughts, famine and economic mismanagement led to the deaths of between 500,000 to 600,000* North Koreans. Recent years have seen an improvement in political relations between both the North and South, and even sporadic improvements with the U.S., which could lead to a less-isolated North Korea in the future; however, the continued testing of nuclear weapons and allegations of widespread human rights violations have drawn widespread criticism from the international community. In 2020, it is estimated that approximately 25.8 million people reside in North Korea.

In 1800, it is estimated that approximately 9.4 million people lived in the region of modern-day South Korea (and 13.8 million on the entire peninsula). The population of this region would remain fairly constant through much of the 19th century, but would begin to grow gradually starting in the mid-1800s, as the fall of the Joseon dynasty and pressure from the U.S. and Japan would end centuries of Korean isolationism. Following the opening of the country to foreign trade, the Korean peninsula would begin to modernize, and by the start of the 20th century, it would have a population of just over ten million. The Korean peninsula was then annexed by Japan in 1910, whose regime implemented industrialization and modernization policies that saw the population of South Korea rising from just under ten million in 1900, to over fifteen million by the start of the Second World War in 1939.

The Korean War Like most regions, the end of the Second World War coincided with a baby boom, that helped see South Korea's population grow by almost two million between 1945 and 1950. However, this boom would stop suddenly in the early 1950s, due to disruption caused by the Korean War. After WWII, the peninsula was split along the 38th parallel, with governments on both sides claiming to be the legitimate rulers of all Korea. Five years of tensions then culminated in North Korea's invasion of the South in June 1950, in the first major conflict of the Cold War. In September, the UN-backed South then repelled the Soviet- and Chinese-backed Northern army, and the frontlines would then fluctuate on either side of the 38th parallel throughout the next three years. The war came to an end in July, 1953, and had an estimated death toll of three million fatalities. The majority of fatalities were civilians on both sides, although the North suffered a disproportionate amount due to extensive bombing campaigns of the U.S. Unlike North Korea, the South's total population did not fall during the war.

Post-war South Korea Between the war's end and the late 1980s, the South's total population more than doubled. In these decades, South Korea was generally viewed as a nominal democracy under authoritarian and military leadership; it was not until 1988 when South Korea transitioned into a stable democracy, and grew its international presence. Much of South Korea's rapid socio-economic growth in the late 20th century was based on the West German model, and was greatly assisted by Japanese and U.S. investment. Today, South Korea is considered one of the world's wealthiest and most developed nations, ranking highly in terms of GDP, human development and life expectancy; it is home to some of the most valuable brands in the world, such as Samsung and Hyundai; and has a growing international cultural presence in music and cinema. In the past decades, South Korea's population growth has somewhat slowed, however it remains one of the most densely populated countries in the world, with total population of more than 51 million people.