Marshall Plan
You know what's bad for the economy? Dropping bombs on it. (Actually, that's true pretty much across the board—although we're huge fans of the bath bomb.)
During World War II, Europe had enough explosives dropped on it to make it only slightly more hospitable than the moon. When the war ended, Europe found itself having a tough time recovering, and the world realized that having an entirely devastated continent wasn't in anyone's best interests.
Who'd have thunk it, right?
What Secretary of State George Marshall and others realized was that dire economic conditions generally result in countries turning to communism or fascism. They didn't even have to look that far into the past. After all, folks like Hitler, Mussolini, and Stalin didn't come to power in thriving, rich societies.
So they had a choice: help Europe recover, or watch World War II get an unnecessary and possibly even more brutal sequel. Since Part Threes are always terrible (*cough The Godfather: Part III cough*) the U.S. chose the Marshall Plan.
The Marshall Plan is an umbrella term for two things. The first was a speech Marshall himself gave at Harvard in front of 15,000 people in 1947. This was where he outlined the need for economic action, and more or less what that meant. The other was a series of laws, the Economic Cooperation Act and Foreign Assistance Act, which took the principles of the speech and turned them into policy.
The basics were pretty simple: the U.S. would send a ton of cash to Europe to fix the place up and jumpstart the economy. The big industrial powers would get the most, since that would help the most people, and allies would get preference over enemies. The biggest recipients of cash, therefore, were Great Britain, France, and West Germany, in that order.
The Marshall Plan even offered money to the Soviet Union and their satellite states. Unsurprisingly, they rejected it, since taking the money would mean the U.S. would have influence over them. And since part of the purpose of the plan was to fight communism, it wasn't like a bunch of communists were going to line up for it. They even had their own version of a plan specifically to fight the Marshall Plan: the Molotov Plan.
The Marshall Plan was in effect for four years, from 1948 to 1952, and afterwards was replaced with other foreign aid plans. It was a resounding success. Every single country that got U.S. money had an economy that was better off than it was before the war even started.