Unlike in South Asia, where the ending of the Cold War did not make much difference to the regional security dynamics, in East Asia it made a big difference. In Southeast Asia the withdrawal of Soviet power and the pulling back of US forces facilitated the shift away from a conflictual bipolarisation and towards a security regime. In Northeast Asia, the confrontation on the Korean peninsula continued, and Japan chose to remain a subordinate partner of the United States. The military confrontation of the Cold War dropped away, but only to give more freedom of action to China, whose weight in the region was increasing rapidly. This encouraged the local states to begin relinking their security affairs on an East Asian scale. The main argument in this chapter is that, by giving more weight to China, the ending of the Cold War opened the way for an external transformation in the regional security architecture of East Asia. From the 1980s economically, and during the 1990s also in a military-political sense, the states of Northeast and Southeast Asia increasingly began to merge into a single RSC. A benchmark date to signal the before and after points of this merger could be 1994–5, when the ASEAN Regional Forum (ARF) was set up, and Vietnam joined ASEAN. This merger had both historical precedents and Cold War precursors as sketched above.