Why did Stalin feel compelled to create puppet states in Eastern Europe?

Stalin created puppet states in Eastern Europe to expand the power of the USSR. It also enabled the Soviet Union to take advantage of these nations' Natural Resources and their industries. The idea that he created the socalled Soviet bloc to protect the USSR from Western Europe and the US, is a convenient way to rationalize his method of imperialism. And, the idea that by controlling the nations of Eastern Europe, he prevented the creation of an anti-Soviet alliance that could become a threat to the USSR falls into the excuse for imperialism stated earlier.

In terms of measuring the validity of the Soviet imperialism argument for Stalin's aggression is fairly easy. For all practical purposes, there is no evidence that the populations of Western Europe made any mass movements into Eastern Europe to be protected from Western imperialism. Quite the opposite, people in these puppet states risked their lives to escape from Eastern Europe, or stage revolutions, such as Hungary did in the mid 1950's.