i've purchased a world war 2 e book which is interesting, it's short/bite sized but to the point. I'm reading about the winter war and im stuck. Here is what's in the book, Stalin, knowing that his country's pact with Germany would not last indefinitely, sought a buffer zone against any future German attack. By June 1940, he had bullied Estonia, Latvia and Lithuania into co-operation, swiftly followed by full annexation. What i don't understand is what is a buffer zone? Also by full annexation, does that mean that those country's became part of Russia?