Obama visit to Asia seen as counterweight to China

FILE - In this March 31, 2014 file photo, South Korean and U.S. Marines aim their machine guns during the U.S.-South Korea joint landing exercises called Ssangyong, part of the Foal Eagle military exercises, in Pohang, South Korea. The U.S. has 50,000 troops in Japan and about 28,500 deployed in South Korea, where it just concluded joint U.S.-South Korean exercises. But Tokyo and Seoul remain at odds over a separate territorial dispute and lingering Korean resentment of Japanese aggression before and during World War II. (AP Photo/Ahn Young-joon, File)