The article discusses how the United States influenced Southeast Asian regional cooperation from 1945 to 1975. It shows how economic cooperation and collective security were linked in the region. The research looks at American, British, and Australian policies and their impact on Southeast Asian regionalism. The study suggests that Southeast Asian cooperation was shaped by both American and Asian policies, reflecting the changes in the region after World War II. This analysis sheds light on the origins of Southeast Asian regionalism and its importance in international relations.