The Marshall Plan, also known as the European Recovery Program and enacted in 1948, contributed to the division of Europe, but most historians believe the Cold War began before the introduction of the Marshall Plan.
Historians tend to trace the Cold War to escalating rhetoric between the Soviet Union and the United States, with a little help from the British, in early 1946. In February 1946, Soviet premier Joseph Stalin delivered an election speech in which he mentioned capitalist hostility. Seeing the speech as potentially indicative of Stalin's intentions vis-a-vis the West, the Truman administration requested that George Frost Kennan, who was charge d'affaires at the U.S. embassy in Moscow, to provided an analysis of Soviet intentions. Kennan produced what came to be as the Kennan Long Telegram. The telegram, which was sent to President Harry Truman and the State Department, suggested that the Soviets were expansionist by nature and that the U.S. needed to focus on the vigor of its own civilization, in hopes of containing the spread of communism. The Iron Curtain Speech, delivered by the former prime minister of Great Britain Winston Churchill in the presence of Truman at Westminster College on March 5, 1946, took a more aggressive tone than Kennan had: it compared Stalin to Hitler, announced an Anglo-American alliance, and urged the American people to take the baton of leadership from Great Britain. The Soviet intelligence apparatus reacted to the speech with great alarm, seeing it practically as a declaration of war. This point was probably one of no return and the Cold War by this time, March 1946, was more or less inevitable. The Marshall Plan was just another step in the unfolding of a policy path upon which the Truman administration had already embarked.
One could, however, make the argument that the Marshall Plan had deeper roots in the tension between the U.S. and the Soviet Union. The Soviet Union had participated in the Bretton Woods Conference in New Hampshire in 1944 but had refused to sign the agreements. Why? The conditions dictated that signatories were to divulge economic statistics and let in western observers as a condition of financial assistance related to reconstruction, to be granted by the International Bank for Reconstruction and Development and International Monetary Fund. The Soviet Union badly needed the assistance but did not trust "western capitalists," whom they saw as greedy warmongers, with the knowledge of the full extent of the devastation the Soviet Union had suffered in the war. Stalin did not want to reveal Soviet vulnerabilities. For this reason, he appealed to the Truman administration for a "no strings attached" loan. The Americans declined and then set up conditions for the Marshall Plan along similar lines as the Bretton Woods Agreements. In other words, the U.S. was intent on using its economic strength as leverage against the Soviet Union and Stalin did his best not to let them do it.
Below, you will find a link with many helpful resources, including links to primary sources from the early Cold War.