IRON CURTAIN
The Iron Curtain was the political, military, and ideological barrier put in place by the Soviet Union. It cut off all ties to Western Europe and any non-communist country. The term Iron Curtain was created by Churchill when he said a speech, and referred to the isolation of Eastern Europe as the Iron Curtain being drawn.
The US responded with not pursuing that side of Europe. The US felt it as threatening that the USSR had such a power over all places that surrounded it.
The USSR was struggling inside of the lines. They were finding it hard to keep up with the needs for their people. Their economy was not getting better, and they were sinking into a hole that would be harder and harder to get out of. They finally "lifted" the curtain, and were reentered into the world.