"The Marshall Plan caused the division of Europe and thus the Cold War." To what extent is this assertion true?
This assertion is hard to defend in any very vigorous way. For the most part, it is not a true statement.
When the United States first floated the idea of what became the Marshall Plan, it explicitly offered aid to the Soviet Union and to other countries of Eastern Europe such as Czechoslovakia and Poland. However, the Soviet Union rejected the aid and required its satellite countries in Eastern Europe to reject it as well. It is possible to argue that the US is at fault for this rejection. This is possible because the US did stipulate that countries that accepted the aid had to meet certain political conditions that the communist countries could not accept. However, it is hard to argue that this was the cause of the division of Europe. It is just as easy to say that the Soviets divided Europe by requiring their Eastern European clients to adopt communist governments.
The true causes of the Cold War are in the mutual distrust between the capitalist/democratic world and the communist world. The two sides each distrusted the other’s ideology. It was this, and not the Marshall Plan, that truly divided Europe and caused the Cold War.