'The Marshall Plan of 1948 is the most important reason why the Cold War started.'
l agree with the statement. The Marshall Plan in 1948 was an extension of the Truman Doctrine (March 1947), which marked the start of American containment policy. While the Truman doctrine provided economic and military aid to Greece and Turkey because of the increased presence and prominence of the communists in these two countries, the Marshall Plan committed the US to give even more economic aid and to reconstruct Europe and its economies regardless of whether the countries were under communist influence or otherwise. The dire economic situation in Europe would provide opportunities for the communists to promote communism as an attractive alternative and solution. To prevent this from happening, the US sought to provide economic assistance to relieve and revitalise the European capitalist economies. The Marshall Plan gave the impression to Europe that it was sincere in helping the European economies, in contrast to the Soviet Union, which was more concerned about its own survival. Though the Marshall Plan was also offered to the USSR and its allies, Stalin was unhappy about it as the Marshall Plan continued to contain USSR's influence in Europe, as accepting it would cause the USSR to accept US influence, and if it refused, the relationship between USSR and its Eastern European allies would be strained. In retaliation, to counter the Marshall Plan, The USSR set up Cominform in Sept 1947 to also provide similar economic aid to all European satellite states, but on the condition of them implementing Soviet style communism, restricting trade with non-communist states. In January 1949, as a response to the Marshall Plan, Comecon was introduced, which further united the economies of Eastern Europe with that of the Soviet Union. The existence of the Cominform and Comecon to counter the the Marshall Plan, led to the emergence of two mutually exclusive and competing blocs of Europe, as most countries were either in the American or the Soviet sphere of influence, and thus Europe became increasing divided along political and economic lines, which marked the start of Cold War bipolarity, which fuelling further tensions and therefore leading to the onset of the Cold War.
I disagree with the statement. While the Marshall Plan and Comecon contributed to the onset of Cold War bipolarity, other events further fuelled tensions between the two such as the division of Germany and Berlin. The USSR and the Allies were determined to continue their own spheres of influences, with the Allies in particular, who saw the importance of Germany's economic recovery. The US and Britain's zones were combined to form Bizonia, and they introduced a new currency the Deutsche Mark to prevent hyperinflation and steady prices of German export products, which in turn led to strong economic recovery in the Western Zones. Stalin then resorted to initiating a blockade on movement into West Berlin by cutting off all land and waterways, as well as communications between Western Berlin and the Western Zones in Germany. Food supplies and electricity was also cut in West Berlin. Stelin aimed to prevent the West from unifying their zones of influence, as well as starving the people in West Berlin into submitting the USSR. However, the Allies then started to transport supplies to West Berlin by air. The Berlin Airlift began, supplying people in West Berlin for the next 11 months. As it was the onset of the Cold War, neither side was willing to resort to any form of military interventions, and by May 1949, seeing that it was a failure, Stalin officially ended the Berlin Blockade. However, this episode further fuelled tensions between Stalin and the Allies because after this episode, the French also merged their zone of influence with the US and Britain, and with West Berlin, this later became the Federal Republic of Germany (West Germany) in May 1949. In response, the Soviets renamed their zone of influence the German Democratic Republic (East Germany) after this was merged with East Berlin. This divide further aggravated the tensions between USSR and the US with its Allies, which further stoked the Cold War tensions.
Overall, I agree that the Marshall Plan was pivotal in starting the Cold War, because the Soviets only responded in retaliation to what the US did. While the Truman Doctrine provided the foundation for the Cold War rivalry, the subsequent Marshall Plan was extensive and excessive enough for the Soviets to respond with Cominform and Comecon, all of which would not have existed without containment and the Marshall Plan. The other further developments such as the Berlin Blockade and Cold War rivalry in other parts of the world were also due to the existence of the Truman Doctrine and Marshall Plan. Hence The Marshall Plan was the most important reason why the Cold War broke out because it led to the ensuing tensions and subsequent actions and events.
(Accept: Disagree because the post WWIl and Stalin's actions in Eastern Europe using salami tactics were more important. Stalin's active intervention and setting up of communist style governments in Eastern Europe caused the Allies to become suspicious of Stalin's motives and led to their reactions and the need for "Containment".