Obama addressed Iran and North Korea nuclear programs at Osan Air Base in South Korea. Obama also discussed free trade agreement with S. Korea President Lee.
Obama, who called the Great Wall 'magical,' leaves with new awareness of US-China interdependence – as well as differing priorities.
Obama is expected to receive a warm welcome in South Korea, where top issues on agenda are North Korea talks and a free trade agreement.
On the second stop of Obama's Asia trip, the president will meet with the 10 ASEAN leaders in a region that welcomes the US presence as a counterbalance to China.
Obama will say that Asia is crucial to answering the world's major challenges – although the US intends to remain a leader across Asia. The president visits Japan, Singapore, China, and South Korea starting Friday.
South Korea accused North Korea of entering its waters and ignoring warning shots, charges the North denies.
A South Korean ship fired on a North Korean vessel after it says the North's ship crossed into the South's waters. The exchange ratchets up tensions before US President Obama's Asia visit, scheduled for mid-November.
North Korea's Kim Jong-il was reportedly "enraged" by TV commercials for beer, quail, and ginseng that he thought echoed China's early moves toward market reforms.
North Korea's announcement that it had processed more nuclear weapons fuel for use in another atomic weapon is seen as an attempt to reinforce its demand that the US engage in bilaterial disarmament talks.