Answer:
to create a buffer zone between itself and the Western powers
Step-by-step explanation:
Buffer zones refers to areas that separate countries which are hostile toward one another.
After the world war II, the soviet union and the western powers involved in ideological conflict regarding Communism vs Capitalism as the proper economic system.
This create a fear among these nations that either of them could launch a military attack to the opponents to won the conflict.
To prevent this, the soviet union take over several countries that located between their territory and the strongest countries in western region (England, United States, France). These countries served as as buffer zone for the soviet union, meaning that the western alliance has to get pass these countries' defense before they can even reach the soviet union. They basically acted as a fortress for the soviet union.