By the late 1990s and beyond, the US-Japan relationship had been improved and strengthened. The major cause of friction in the relationship, e.g. trade disputes, became less problematic as China displaced Japan as the greatest perceived economic threat to the U.S. Meanwhile, though in the immediate post–Cold War period the security alliance suffered from a lack of a defined threat, the emergence of North Korea as a belligerent rogue state and China's economic and military expansion provided a purpose to strengthen the relationship. While the foreign policy of the administration of President George W. Bush put a strain on some of the United States' international relations, the alliance with Japan became stronger, as evidenced in the Deployment of Japanese troops to Iraq and the joint development of anti-missile defense systems. The notion that Japan is becoming the "Great Britain of the Pacific", or the key and pivotal ally of the U.S. in the region, is frequently alluded to in international studies, but the extent to which this is true is still the subject of academic debate.