Key US ally’s military shrinks by 20% due to population decline

South Korea released a report on Sunday that showed the size of its military has decreased by 20% over the past six years. Officials indicated that the major decrease in the South Korean military is due to a major decrease in the population of enlistment-age males caused by the lowest birthrate in the world.

The report by the South Korean Ministry of National Defense, which was obtained by Reuters, showed that South Korea’s military has decreased from roughly 563,000 active-duty troops in 2019 to roughly 450,000 troops. Reuters reported that the size of the South Korean military has continually decreased since the country had roughly 690,000 troops in the early 2000s.

According to Reuters, the decrease in males eligible for service in the South Korean military has also resulted in a decline in the number of officers in the military, which could lead to operational challenges if the decline continues.

Reuters reported that based on 2022 estimates, the North Korean military has approximately 1.2 million active-duty troops, compared to South Korea’s 450,000 troops. According to The BBC, the report by the South Korean Ministry of Defense notes that the size difference between the two militaries leaves the South Korean military in a “structurally difficult position to succeed in defence.”

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According to The BBC, with limited exceptions, all able-bodied males in South Korea are forced to serve in the military for 18 months. However, Reuters reported that the number of enlistment-age males dropped significantly as the population of 20-year-old males decreased by 30% from 2019 to 2025.

Reuters reported that South Korea’s fertility rate was the lowest in the world in 2024, while its population remains one of the fastest aging populations in the world. According to the outlet, South Korea’s government believes its population, which was approximately 51.8 million in 2020, will decrease to 36.2 million by 2072.

While Reuters reported that South Korea’s 2025 defense budget, which is over $43.9 billion, is estimated to be greater than the North Korean economy, the outlet noted that the South Korean military is currently 50,000 troops below the number of troops the Ministry of National Defense believes the country needs to be prepared for future military conflicts. Sunday’s report indicated that 21,000 of the additional 50,000 troops needed include non-commissioned officer ranks.