Joint-training with distant nations is nothing new to the US military. It not only builds relationships between foreign powers, but also familiarizes them with each other's standard operating procedures in the event of a military emergency.
As one of these important allies, the Republic of Korea has continuously conducted training operations with the US military in the effort to stabilize the Korean peninsula and its neighbors in close proximity. Considering that North Korea and its southern counterpart are technically still at war, this may prove to be a necessary task.
One of these training events was recently conducted on July 6, 2016, in Pohang, South Korea, which included 500 US Marines from Okinawa, Japan, and 800 South Korean Marines.
Check out the photos of these two nation's Marines in action: