The Iron Curtain was the political and physical boundary that divided Europe from the end of World War II in 1945 until the end of the Cold War in 1990/1991. East of the Iron Curtain were many small states controlled by the Soviet Union, in 1955 formally allied by the Warsaw Pact. Many nations to the west of this geopolitical divide were NATO members. Over time these economic and military alliances developed into broader, more entrenched, cultural barriers; widespread distrust on both sides deepened. Initially, the term "Iron Curtain" was a literal description of physical barriers such as razor wire, fences, fortified walls, minefields, and watchtowers along the western border of the Eastern Bloc. The term later took on a broader, metaphoric meaning perceived as a generalized "differentness" of ideology, economy, government, and way of life that emerged when the Cold War severed earlier cultural connections between European populations.