U.S. participation in NATO was a break with tradition, since the United States for the first time set itself up to automatically get involved in foreign conflicts--something that was very unnerving for a country of people who for most of American's history had been very isolationist.
The best option from the list would be that the Marshall Plan intended to "<span>help Europe's economic recovery</span>" after World War II, but the main reason it did this was to provide financial aid to countries in Europe that were at risk of falling to communism.