The top dogs in that part of the world were the Japanese, they invaded Korea around the 16 century and were constantly raiding their towns and seaports. Finally they conquered the peninsula at the end of the 19th century, deposed the emperor and made Korea and portions of China puppet states.
Japan was defanged after WW2 but with time everything changes and who knows, it might in the strategic interest of the US to let Japan rearm again.