Answer:
The phrase "The Iron Curtain" is associated with the Cold War and it refers to the closed nature of the Soviet Union. It evokes the invisible boundary line that separated Eastern and Western Europe after the end of WWII until the end of the Cold War in 1991.
Explanation:
The Iron Curtain refers to the divisions between East and West after WWII when the Soviet Union made efforts to block itself and all its satellite states off from Western influence. There were military alliances developed on the Eastern side of the Iron Curtain with the Warsaw Pact and on the Western side with NATO. There were some physical manifestations of the border or divide between East and West, the most symbolic being the Berlin Wall.