The guiding assumptions of modern American foreign policy were set out in a document written in 1950 for president Harry Truman. NSC-68 as it was called (the paper was prepared at the National Security Council) was Washington’s answer to Soviet communism. At its core was a belief that US national interests were best pursued through international leadership. This is the foundation stone to which Donald Trump has taken a sledgehammer.
Much of NSC-68 focused on countering the military threat from the Soviet Union. Signed off by Truman at the start of the Korean war, it was the basis for a rapid build-up in US defence spending. But mindful of how the national mood could turn to isolationism, it also aimed to quash the idea that America could retreat again into its own hemisphere.
Thus: “Our overall policy at the present time may be described as one designed to foster a world environment in which the American system can survive and flourish. It therefore rejects the concept of isolation and affirms the necessity of our positive participation in the world community.” Here was the strategic rationale, lasting beyond the cold war, that enmeshed the US in the fabric of what we call the west.