Truman Doctrine
The 1947 pledge to support any free people resisting subjugation, which turned American aid to Greece into an open-ended commitment to contain communism worldwide.
On March 12, 1947, Harry Truman asked Congress for four hundred million dollars in aid to Greece and Turkey. The money was almost beside the point. The sentence that mattered was this one: it must be the policy of the United States to support free peoples who are resisting attempted subjugation by armed minorities or by outside pressures. It named no country and set no limit, and for the next forty years American presidents used it to justify commitments from Seoul to Saigon.
The immediate problem
The trigger was a British confession. On February 21, 1947, London informed Washington that it was broke and would stop underwriting Greece within six weeks. Greece was in the middle of a civil war between a shaky royalist government and communist-led insurgents supplied from Yugoslavia, Albania, and Bulgaria. Turkey, meanwhile, was under Soviet pressure to concede bases and joint control of the straits between the Black Sea and the Mediterranean.
The strategic question was not really Greece. It was whether the United States would step into the space a collapsing British Empire was vacating, and do it in peacetime, with a Congress elected on promises to cut taxes and bring the boys home.
Scaring hell out of the country
The administration concluded it could not sell this on the merits. In a famous briefing, Under Secretary of State Dean Acheson told congressional leaders that Soviet pressure on the straits could rot Iran, then Asia Minor, then Egypt, and then all of Europe, like a bad apple infecting a barrel. Senator Arthur Vandenberg, the Republican whose support was essential, told Truman that if he wanted the money he would have to scare hell out of the American people.
So the speech dropped the details of Greek politics, which were awkward, and framed the request as a global choice between two ways of life, one based on the will of the majority and the other on the will of a minority forcibly imposed. Congress passed the aid in May.
What it committed the country to
The doctrine is where American containment became national policy rather than an argument inside the State Department. It was matched three months later by the Marshall Plan, the economic half of the same strategy, and two years later by NATO, the military half.
It also carried two problems inside it from the start. The first was that its language was universal while American power was not. If every free people resisting subjugation had a claim on Washington, the commitment had no natural stopping point, and critics from Walter Lippmann onward warned that the country would end up defending places it could not name for reasons it could not explain. Vietnam is the standard illustration.
The second was that free was doing heavy lifting. Greece's government was authoritarian and its security forces brutal; Turkey was a one-party state. Over the following decades the doctrine's logic underwrote support for a long line of unpleasant regimes on the grounds that they were on the right side of the larger contest. That tension between the stated principle and the actual clients ran through the entire Cold War and did lasting damage to American credibility in the countries on the receiving end.
The doctrine worked in its immediate purpose. Greece and Turkey stayed out of the Soviet sphere and both joined NATO in 1952. Historians generally treat March 12, 1947 as the day the United States formally declared the Cold War, and it is worth noticing what kind of declaration it was: not a threat, but a promise, made in language expansive enough that every successor could read his own war into it.