The Cold War/How did it all start?
After six long years of bloodshed, World War 2 had finally come to an end. Europe was a complete junkyard - dead bodies littered the streets, buildings were destroyed, rubble was everywhere - you probably get the idea now. But the nation that was affected most by this destruction was the Soviet Union.
Over 20 million Soviet citizens died in the conflict and hundreds of thousands of buildings lay in ruin. The damage was horrendous. Stalin, the Soviet leader at that time, was absolutely furious. He didn't want his country to be ever again invaded by the countries in the West, like it had been by Nazi Germany - and he would go to practically any length to prevent this from happening again.
He decided that he would make Eastern Europe his "defence layer" to protect the USSR from any future military threat from the West, by putting communist governments there that would directly obey orders from Moscow.
The response and the "Iron Curtain"
The Americans and British were angered at these actions. They had been fighting for a free, democratic Europe that would be liberated from the "evil" and murderous ideology of Nazism. But when they found out that the USSR was forcing the countries in Eastern Europe to accept communism, by stationing their troops right next to the polling stations in order to intimidate the voters, they felt that they their very cause, which had cost the lives of millions, had been simply put to waste. They felt that their former ally had betrayed them and grabbed this opportunity to spread and enforce communism throughout the world.