Help please, this is a pretty easy question.

USA believed that the future of US prosperity and democracy was at risk if the expansion of communism across Europe and Asia.
•1954, French were driven from their colony and the US feared that communism would spread.
•Communism was spreading and by 1956 the Soviet Union, China, Eastern Europe and North Korea all had communist governments
•Americans felt increasingly threatened by the spread of communism. 'This fear was based on the "domino theory" where if one country became communist others would follow. If South Vietnam fell it would be followed by the countries near by.
•1964, the North Vietnamese opened fire on the US navy and the US Congress gave the new President, Johnson, the necessary powers to deal with the problem