Prime Minister Yukio Hatoyama gave up on a bedrock campaign pledge and accepted a longstanding U.S. proposal for positioning American troops in Japan, backing down from a battle with Washington as the two nations grapple with North Korea's aggression and China's rising power in the region. The move hands the Obama administration an important foreign-policy victory, allowing Washington to avoid what, for a time, appeared to be an unwelcome need to rearrange its regional defense strategy in North Asia while fighting two wars and navigating other tense diplomatic and economic tussles around the world. Beyond the specifics of the Marine...