One of the top issues cited was the East China Sea, which Japan and China both claim part of. The American and Japanese senior officials said their governments reiterated their strong opposition to China's "intensifying attempts to unilaterally change the status quo by force or coercion." [...] Japan and South Korea, two countries where the United States has troops stationed, are among the most worried. Wary of a potential war involving China, North Korea or both, many Japanese and Korean officials see the presence of U.S. troops and weapon systems as a crucial deterrent.