Ever since its birth in the 1970s, G2 has gone through four versions-a US-Germany G2, a US-Japan G2, a US-EU G2 and the most recent US-China G2. The choice of four different countries or regions in different periods shows American strategists' sensitivity to the change of power in the international system and their openness to foreign policy alternatives. The four versions of G2 also reveal great similarities in America's foreign policy considerations: as each of these versions was floated in a time when the United States was bogged down in domestic and international difficulties while the other country/region was on the rise, they were part of America's burdensharing strategy, encouraging others to take on greater international responsibilities in the UScentered international system.