The United States is continuing a decade old effort to reorganize its remaining forces in South Korea. This now involves expanding the only remaining U.S. Army division (the 2nd Infantry) with the addition of a South Korean mechanized infantry brigade. This gives the division two combat brigades, the other one being American. South Korean officers and troops are also being added to division headquarters. The division will still be commanded by an American and the South Korean brigade will still belong to the South Korean Army but will serve as part of an American division rather than a South Korean one. This form of cooperation is actually part of a trend that has been underway for over 60 years.
One aspect of the American reorganization, began in 2010, was to make it easier to move American forces into, and out of, South Korea in a hurry. The idea is to make American and South Korea units more effective in working together. The main army headquarters for American forces in South Korea, the Eighth Army, is being upgraded with staff and support personnel so that it could quickly command twelve or more combat brigades, and all the support forces needed for that many combat troops.
Since the 1990s the U.S. has been working to transfer supreme military command in South Korea to the South Koreans. However, as North Korea developed nuclear weapons, built more long range ballistic missiles and threatened to use chemical weapons South Korea sought more potential help from the U.S. So while U.S. troop levels in South Korea are at record lows, preparations are being made to increase them, a lot, in a short period of time.
American troops have been in South Korea for over sixty years and the U.S. has always said it would stand by its South Korean ally. But the numbers tell a different tale. At the end of the Korean War, in 1953, there were over 350,000 U.S. troops in South Korea. Within a year, that shrank to 223,000, and by 1955 it was only 85,000. By the mid-60s it was 63,000 and a decade later there were only 42,000. There it stayed for over two decades. Then came the September 11, 2001 and the war on terror. By 2004 the U.S. force in South Korea was down to 37,000. In 2006 that dropped to 30,000 and in 2008 it went to 28,000.
Since 2008 the U.S. has been moving its forces away from the DMZ (Demilitarized Zone) that forms the border between North and South Korea. This makes it possible to let troops bring their families with them. That means troops will stay for three years when assigned to South Korea, instead of the previous 12 month unaccompanied (by family) tour of duty. By keeping troops around for three years, they get to know about South Korea and their counterparts in the South Korean military.
Meanwhile the South Korea Army was undergoing changes. While South Koreans do not like the Japanese South Korean military traditions were largely inherited from the Japanese, who, before World War II, had a rather brutal attitude about how soldiers were handled. During World War II, many Koreans were allowed to join the Japanese army as support troops, and were subjected to the brutal Japanese discipline. Sergeants were allowed to use physical violence freely, and soldiers who had been in longer, even a few months longer, got away with similar abuse of the more recent recruits. American soldiers who saw South Koreans do this after World War II, and many did (as U.S. and South Korean units were often based close together), were appalled.
South Korea has had conscription for the last sixty years, so most adult males have served 2-3 years in uniform. In addition to the brutality, military life is regimented 24/7. Living conditions are not all that great, and pay is minimal. For years, there have been suggestions, from veterans, that South Korea adopt practices similar to the Americans. This is because, since the Koran 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. During the Korean War over 6,000 KATUSAs died while serving with American units. There are still several thousand KATUSAs assigned to U.S. units.
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). But there are few disciplinary problems.
The KATUSAs are usually smarter than the average 18 year old conscript and see service in an American unit as an excellent opportunity to improve their English skills, and learn more about Americans. This helps later on, for getting into college and/or getting a good job. Also, the living conditions are much better, and the work generally more interesting. On the downside, KATUSAs come to their American units right out of basic training, without any specialized training. So KATUSAs generally don't get any high tech jobs, and have to be trained for whatever work they do get assigned. But since most of the KATUSAs are good students to begin with, and ambitious, there are often opportunities to train them for some pretty complex jobs. This has changed in the last few decades as education levels among draft age South Koreans increased and now many KATUSAs perform skilled jobs. All this was part of an evolution of the South Korean military to one more similar to those found in the West. South Korea began equipping its troops like their American counterparts in the 1990s, but often using high-tech weapons and equipment made in South Korea. Naturally South Koreans looked to their American allies, who were also using such equipment, for insight on how to get the most out of all this new gear. So putting an American and South Korean combat brigade in the same division was not such a radical idea when you consider that both brigades use similar (and sometimes identical) equipment and often use it the same way.