What was the Iron Curtain, and what did it do?

The Iron Curtain was a term used to describe the
separation between West and East during the Cold War. Eastern countries controlled by
the Soviet Union during the Cold War were said to be "behind the Iron Curtain." The
phrase was used first by Winston Churchill in a speech at Westminster College, who
said

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.

These countries were
controlled by the Soviet Union to the extent that they were considered only satellites
of the Soviets. The Soviet Embassy in East Berlin was the largest government building in
the city, as all of East Germany was governed from there. It was called an "iron
curtain" because it was a closed society. Information to and from the west was tightly
controlled; there was little knowledge within the west of events in that area, and vice
versa. In a metaphorical sense, the Iron Curtain was them the line between the
Republican west and Communist East in Europe.