The Iron Curtain is an expression describing the divide between the two sides involved in the
Cold War, in particular it is used in NATO countries in reference to the countries and people within the Warsaw Pact countries.
The best known use of the term probably comes from Winston Churchill during a speech shortly after the end of World War 2:
From Stettin in the Baltic to Trieste in the Adriatic an "iron curtain" has descended across the continent. Behind that line lie all the capitals of the ancient states of Central and Eastern Europe. Warsaw, Berlin, Prague, Vienna, Budapest, Belgrade, Bucharest and Sofia; all these famous cities and the populations around them lie in what I must call the Soviet sphere, and all are subject, in one form or another, not only to Soviet influence but to a very high and in some cases increasing measure of control from Moscow.
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From '
A Time For Choosing':
We cannot buy our security, our freedom from the threat of the bomb by committing an immorality so great as saying to a billion now in slavery behind the Iron Curtain, "Give up your dreams of freedom because to save our own skin, we are willing to make a deal with your slave masters."
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Iron Curtain (Wikipedia)