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South Korea's active-duty military has contracted sharply over the past six years, falling by 20% to around 450,000 personnel, as the pool of young men eligible for mandatory service continues to dwindle. According to a Defense Ministry report released Sunday by lawmaker Choo Mi-ae's office, the decline stems from the country's record-low birthrate, which has reduced the number of 20-year-old men, the primary age for enlistment, by 30% since 2019. In 2025, that cohort stands at roughly 230,000.
The shrinking manpower is creating shortages across the ranks, with the military now about 50,000 troops below the level deemed necessary to maintain readiness. The shortfall includes approximately 21,000 non-commissioned officers, raising concerns about operational effectiveness if the trend continues.
South Korea's armed forces have been steadily decreasing in size since the early 2000s, when troop numbers hovered around 690,000. In 2019, the total stood at about 563,000, before dropping more rapidly in the years that followed. By contrast, North Korea is estimated to have roughly 1.2 million active-duty soldiers, according to ministry data from 2022.
Officials have partly offset the manpower decline by shortening mandatory service periods, from 36 months in the aftermath of the Korean War to the current 18 months, citing enhanced capabilities from a strong alliance with the United States and a rapidly advancing domestic defense industry that has become a major arms exporter.
Despite a 2025 defense budget exceeding 61 trillion won ($43.9 billion), larger than North Korea's estimated GDP, the personnel gap remains a pressing concern for military planners.
Demographic forecasts paint an even more sobering picture. South Korea's fertility rate fell to a world-low 0.75 in 2024, meaning the average woman is expected to have fewer than one child in her lifetime. The country's total population, which peaked at 51.8 million in 2020, is projected to decline to 36.2 million by 2072, according to government estimates.
The Defense Ministry warns that unless new measures are implemented, the shrinking manpower pool could undermine South Korea's ability to respond effectively to future security threats, even with technological and strategic advantages on its side.
