The Domino Theory if one eastern European country fell Truman feared more would follow
They were afraid of losing control of eastern Europe.
All of Eastern Europe.
The soviets had expected to win a quick victory
The economic and technical assistance offered by the Marsall Plan was not accepted by the Soviets and it's satellites in Eastern Europe.
They were afraid of losing control of eastern Europe.
At the conclusion of WW 2, the Western allies sought democratic governments for Eastern Europe and basically for all of Europe. The Soviets under Joseph Stalin had other ideas. Their armies essentially occupied the Eastern nations where they had driven out the Nazi armies. The Soviets had an expansionist ideology and installed communist governments in the nations of Eastern Europe. This included East Germany.
The Soviets (Russians) had already over-run those positions by wars end. What they had, they kept.
When the Soviets marched through eastern Europe they occupied it and therefore it was communist.
They were afraid of losing control of eastern Europe.
Eastern Europe is 'poorer' than western europe, during the war they were helpless and were taken over by Germany or the Soviets, with the fall of both empires countries taken by Hitler and Stalin suffered and were left to fend for themselves. The countries in the East have started to pick themselves up in the recent decades and they each support their neighbours,places like Azerbaijan are not as poor any more and it fact some of the more developed cities can be found in Eastern Europe.
The US states promised to withdraw from Western Europe if the Soviets withdrew from Eastern Europe under its foreign policy of containment. This policy was to prevent the spread of communism abroad.
The Soviets went bankrupt, their system of government wasn't working, the Berlin Wall came down in 1989, the Soviets themselves collapsed in 1990.