American troops have been stationed in South Korea since the end of the Korean War. Technically, the North and South are still at war, but neither have broken the delicate cease fire for decades besides for a few small skirmishes. Both sides are afraid to reawaken all out war, yet refuse to lower their poker face. As a result, American troops are still stationed in South Korea today for training purposes, moral support, and as a sign of strength.
So what do American Marines do in South Korea? They have drum battles with their Korean comrades of course!