ASEAN is in danger of becoming marginalized as East Asian security becomes increasingly shaped by such volatile flashpoints as a nuclear North Korea and a South China Sea increasingly dominated by quarrels over sovereignty and maritime security. Accordingly, the notion of "ASEAN centrality" is now being seriously challenged and is unlikely to prevail against the growing bipolar security environment shaped by China and the United States. ASEAN and other Asia-Pacific states could gravitate toward one of five alternative order-building scenarios: (i) A Sino-American condominium that defines and accepts each other's geopolitical sphere of influence; (ii) The replacement or substantial revision of the United States' bilateral alliance system with the expansion of multilateral norms and instrumentalities; (iii) The gradual predominance of an "Asia for Asians" concept led by China but endorsed by a substantial number of Southeast Asian states; (iv) Effective balancing and hedging by smaller states and "middle powers", leading to eventual great power acceptance of a regional power equilibrium; and (v) An intensification of regional "community building" via an amorphous but wide-ranging series of economic, ideological and strategic compromises to make war unthinkable and to strengthen regional interdependence. However, none of these five scenarios is likely to predominate in a literal sense. Instead, the "realist" explanation for understanding security in the region is the most accurate forecast for understanding an East Asian security environment that is becoming increasingly disorderly. ASEAN can still play a constructive -- if not central -- role in shaping East Asia's strategic environment by working with China and the United States to strengthen confidence-building in regional security politics and to encourage their respect for strategic constraint.