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% 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 Defense 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.

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.