1) The US attempted to remain on good terms with their allies. It was Soviet suspicion and aggression that caused the break up of the Grand Alliance.
2) The US and Western democracies were as responsible for the breaking up of the Grand Alliance. The US kept holding the USSR to a higher standard of democratic behavior than was practiced in either the US or British colonies.
3) US diplomats allowed the Soviet Union to walk all over them. Had the Americans been tougher with the Soviets, the USSR would have backed down and been far less of a menace to world peace in the future.
IB prompts will often include "to what extent were ideological/economic issues at the heart of the Breakdown of the Grand Alliance." When addressing the stance you have taken, keep these thoughts in mind.
Atlantic Charter
Andrei Vyshinsky Soviet Criticism of Marshall Plan and Truman Doctrine
Kennan's Long Telegram
Novikov's Assessment of Americans
The Marshall Plan Speech
Truman Doctrine
Iron Curtain Speech