It is best to start off by defining what the "Iron Curtain" was. The "iron curtain" was the division of Europe after World War II into two distinct ideological camps. The "iron curtain" basically divided Europe into east and west physically, ideologically, and economically.
On the east, the Warsaw Pact united the nations together and the Soviet Union was the most important. On the west, the North Atlantic Treaty Organization (NATO) united the countries. The United States was the key member in this alliance.
On another level, we can say that ideologically, the east was governed by communism and the west was governed by capitalism. More specifically, those under NATO and those under the Warsaw pact sought to gain countries to ally with them.
Finally, the cold war ended in 1989 and the walls began to crumble.