There are still several nations with conscription laws, and some of them expect their citizens, no matter where they may be living overseas, to come home to do their time in the armed forces. Sometimes this causes interesting problems. Take two Korean-Americans (age 21 and 22, one a U.S. citizen, the other a legal resident) who had enlisted in the U.S. Army. One was stationed in Germany, the other in South Korea. The South Korean Military Manpower Administration (which handles conscription matters) found that both of these fellows had gone and joined a foreign military before doing their time in the South Korean armed forces. This was a no-no, and police were sent to grab the two when they discovered that both of them were in South Korea. One was assigned to an American army unit in South Korea, while the other was on leave from his unit in Germany. At this point, the American military intervened. There is a treaty between the U.S. and South Korea, covering how Americans are handled when they have violated South Korean law. But no one had ever seen a situation like this before. The Americans got their two Korean-American troops out of the clutches of the Military Manpower Administration, for the moment, anyway. South Korea is demanding that these two fellows do their conscript service before they turn 35, or else they will be in violation of South Korean law. However, it was noted that, if the two of them stay in the American military until they are 35, they may be home free.
Further complicating the issue is the growing unpopularity of conscription in South Korea. It's also common knowledge that serving in the American army is much easier and more comfortable than doing so in the South Korean army. This is because, since the 1950-53 Korean war, over half a million South Korean soldiers have served in American units as KATUSAs (Korean Augmentation to the U.S. Army). South Korean conscripts who speak passable English are eligible for this, and it is a much sought after assignment. The KATUSAs remain part of the South Korean army, but report to American units and are given a job that would otherwise have to be performed by an American soldier. The KATUSAs are treated just like the American troops, living in the same barracks, eating in the same mess halls and getting the same medical care. However, there are South Korean officers and NCOs available for any disciplinary problems, and to administer pay and other personnel matters (like leave). KATUSA assignments are much sought after, and there have been some recent scandals when parents were caught paying bribes to get their sons into the KATUSA program.
The military and civilian lawyers are trying to work it all out.