1: he used salami tactics which is the concept of dividing and conquering opposing alliances.
2: attlee and Truman made it very clear at Yalta and Potsdam the Eastern European country should have freely defined States and government. After Stalin broke that agreement the US offered marshal aid to any countries in eastern Europe. Stalin forbade any countries directly or indirectly controlled by the Soviets to accept the aid.
3: I do not believe they are to blame fully. their reactions to Soviet expansionism sparked the Cold war but if the Soviets agreed and stuck by the pack they made, the us would not have had to react at all so the base of the problem was caused by the Soviets but the spark was caused by The Americans
