The writing has been on the wall for a long time: South Korea's birth rate has dropped throughout much of the past decade, spelling trouble for the military as regional threats and global conflicts simmer.
Now, a new report has found that the number of South Korean troops declined by 20 per cent in the past six years, in large part because of the dwindling pool of young men – reflecting the shrinking workforce and swelling elderly population in one of the world's most rapidly aging countries.
The Defence Ministry report attributed the drop to "complex factors" including population decline and fewer men wanting to become officers due to "soldier treatment." The report didn't elaborate on that treatment but studies and surveys have previously highlighted the military's notoriously harsh conditions.
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As of July, the military had 450,000 troops, it said – down from 563,000 in 2019.
"If the number of standing army (members) continues to decline, there can be difficulties in securing elite manpower and limits in operating equipment," warned the report, shared last week by lawmaker Choo Mi-ae.
The news comes at a bad time for South Korea, a key Western ally which hosts huge numbers of US troops and has a mutual defence treaty with Washington.
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Just across the border, neighbouring North Korea has sent tens of thousands of soldiers to fight for Russia along the front lines with Ukraine – raising fears that Moscow may share advanced military technology with Pyongyang in exchange, violating international sanctions.
Meanwhile, North Korea's ruling Kim family has continued blasting hostile rhetoric, threatening to destroy South Korea with nuclear weapons if attacked and warning that Seoul remains "the enemy."
However, experts say, that doesn't necessarily mean North Korea's military is better off.
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The North is facing its own population woes and birth rate decline – and its technology lags far behind the South, which is now hoping to plug the shortfall in military recruits through innovation.
"South Korea is incomparably far ahead of North Korea in terms of conventional weapons," said Choi Byung-ook, a national security professor at Sangmyung University. "We have smaller troops now, but I like to say 'small but strong military,' that's what we need to become."
Double the babies, triple the soldiers
On the surface, North Korea has a few advantages.
It's one of the world's most heavily militarised nations, with up to 1.3 million armed forces personnel, according to the CIA World Factbook. That's nearly three times higher than South Korea's troop numbers.
Those troops also serve in the military for far longer – an average of 10 years, which allows them to have higher "unit cohesion (and) knowledge of each other's capabilities," said Sydney Seiler, senior adviser to the Korea Chair at the Centre for Strategic and International Studies.
By contrast, there's "really not much advanced skills that you can develop" within the year and a half that most South Korean conscripts serve, Seiler said.
North Korea's fertility rate – defined as the average number of children born to a woman in her lifetime – is also far higher, at 1.77 in 2025 compared to South Korea's rate of 0.75, UN data shows. The North has been having more babies per year than the South since 2018, said Jooyung Lee, senior economist at the Bank of Korea Economic Research Institute.
But the full picture is more complicated, experts told CNN.
For one, South Korea has a reserve force of about 3.1 million men. While their training may be basic, it would give them the numbers needed for potential warfare – and that's not including the 28,500 US troops stationed in the country.
Pyongyang is also facing its own population problems, with its fertility rate dipping in the last few years after the pandemic. The nation's authoritarian leader, Kim Jong Un, pointed to the problem at a national conference of mothers in 2023, urging them to "give birth to many children" as a patriotic duty.
That could bode ill for a highly isolated nation with an economy that relies on labour-intensive industries like agriculture and mining, said Lee.
It's hard to tell how much this has impacted the North Korean military so far. But the fact that Pyongyang has sent tens of thousands of troops to fight for Russia suggests Kim "doesn't feel concerned about not having enough soldiers on board to do the task of defending the homeland," Seiler said.
Their military has also enlisted more women to fill whatever gaps do exist. This trend began near the turn of the century after a previous dip in fertility, Lee said, with the proportion of female recruits now reaching as high as 20 per cent by some estimates.
Many are younger women serving in the military's communications, administrative and anti-aircraft artillery sectors, said Lee, who has interviewed many North Korean refugees who fled the country. Meanwhile, middle-aged and older women have been mobilised to fill gaps in other civilian sectors.
By contrast, women are not conscripted in South Korea – a controversial point that has stoked resentment among some young Korean men who argue their mandatory service puts them at a disadvantage in their studies, careers and personal lives.
As of 2023, volunteer females accounted for only 3.6 per cent of the entire military, according to the Defence Ministry.
The way forward
Some experts have suggested that conscripting more women could solve South Korea's problem, which the Defence Ministry has not ruled out. But Choi, the national security professor, argued the country needs to move away from the idea of increasing its manpower – and instead focus on advancing its technology and making the troops elite.
"I don't personally agree with opinions that we must have a large number of troops because North Korea does," he said.
"The size of our troops has decreased and there are not many options to increase it … I think we need to take this crisis as an opportunity as South Korea is in the route of becoming a science technology powerhouse."
On the battlefields of Europe, Ukraine has shown firsthand how an out-manned and out-gunned military can still hold back and inflict painful losses on a much larger opponent by embracing new and affordable technology.
Tools like drones and cyber-warfare could help decrease South Korea's reliance on infantry and artillery, Seiler said. AI-assisted and autonomous systems could further boost a shrinking military, said Leif-Eric Easley, a professor of international studies at Ewha Womans University in Seoul.
Choi pointed out that South Korea spends far more on defence than the North, and conducts many military drills including with allies like the US – making it better equipped in overall combat readiness.
However, Seiler warned, at the end of the day "you still need people. There's no robots or automation that can replace a trained soldier, airman, marine." Easley agreed, saying South Korea's military would still face shortages in manpower in the event of war.
And a broader challenge remains: how do authorities change cultural attitudes toward the military within South Korea?
While people can volunteer to become professional cadres who serve longer terms and train with more advanced weapons, the number of applicants has dropped steadily over the years.
High-profile cases of hazing, bullying and harassment within the South Korean military may have contributed to negative perceptions of the force.
In recent years, the government has loosened restrictions on conscripts – including allowing them to use cell phones at certain times of the day – and offered a longer civilian service alternative to conscription.
But that's not enough, said Choi.
"We need to improve military welfare and fighting spirits as a whole," he said – adding that supporting the current size of the military will become even harder in the coming decades as the population declines further.
"By 2040s, even maintaining 350,000 troops will be difficult, and that is why we need to establish an optimized manpower structure system … as soon as possible."
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