It fell to President Harry S Truman to launch the US response to Soviet expansionism, after two years of growing tensions. He announced Washington would "support free people who are resisting attempted subjugation by armed minorities or by outside pressures". The implications were huge: the US would abrogate the isolationism that had governed its foreign policy before the Second World War, and into which it had started to retreat; and it would join in a global conflict with the Soviet Union. "I would not recommend it except that the alternative is much more serious," said the president.
Truman's rallying cry led to Marshall aid, the huge programme of economic assistance to Europe; to the formation of the North Atlantic Treaty Organisation in 1949, the defence pact that linked America to Europe; and the return of US troops to Europe.
None of this was a foregone conclusion in 1947. After the Second World War ended, there had been a period of uncertainty between the West and the Soviet Union, which had been, after all, a wartime ally. America tried a variety of approaches, but Russia was aggressively promoting communism in Eastern Europe and a confrontation was building up.
Truman's words were to some extent prompted by Britain, then a major power. Britain had been providing military and economic assistance to Greece and Turkey, both threatened (in the view of the West) by Communist subversion. But the disastrous winter of 1946-47 and Britain's economic collapse led it to withdraw this in early 1947. America was stepping in to fill the gap left by Britain, an event repeated many times over the following decades.
The underpinnings for a tougher stance had already been laid by diplomats in Moscow who believed the Soviet Union could not be restrained in conventional diplomatic ways. George Kennan of the State Department, and Sir Frank Roberts, Britain's ambassador in Moscow, had both written long analyses of the situation, and reached similar conclusions. The result was the policy of containment, which the West maintained for 40 years.
The Cold War's end has left a security vacuum in Europe. Nato is trying to fill it by expanding; Russia resists andwarns of a new Cold War. Some in the West are warning that the new threat is China, or Islam. But no great issue has emerged to replicate the global struggle between West and East.
The institutions that flowed from Truman's speech, US forces in Europe and the transatlantic alliance, are still there; but for how much longer?