Why did the us offer aid to europe in the form of the marshall plan, and why did the ussr refuse marshall aid for itself and its allies?

The United States offered $13 billion in economic aid to countries like France, Great Britain, Turkey, and Greece in order to ensure economic stability and to stop the spread of communism. After World War II, the US was worried about the Soviet Union and their communis system spreading to other European countries. This is why they gave these countries aid. This is also why the Soviet Union refused it, as they realized the US’s intentions at this time.