Although they share a common ally, history and politics keep Japan and South Korea at arm’s length and severely limit their defense cooperation. Since at least the mid-1990s, American realists—and not a few Japanese and South Korean analysts—have anticipated that the regional environment, growing steadily more dangerous, would bring these status quo democracies closer together, not least because Washington would drive them to cooperate. Moreover, since Japan has not contended for regional hegemony and since its defense budget has not increased as fast as China’s, South Korea ought to be reassured and feel less threatened. Indeed, although Seoul sees Beijing as a critical (if often unhelpful) intermediary in peninsular affairs, China poses clear challenges for both it and Tokyo. North Korea and the remarkably rapid development of its WMD capabilities pose an unambiguous threat to both of America’s Northeast Asian allies. South Korean President Roh Moo-hyun and Japanese Prime Minister Koizumi Junichirō agreed to meet annually in 2004, but Koizumi’s visits to the Yasukuni Shrine forced Seoul to take this off the table. The meetings were back on when Lee Myung-bak took office, but canceled again by Park Geun-hye.1 Washington has pressed them to cooperate, but only with intermittent success.