In the 1950s and 1960s, us leaders feared that if they did not intervene, countries such as vietnam would ally with france. ask their neighbors to become democratic. fall to communism. believe in the domino theory.

The correct answer is - fall to communism. This was, so called 'domino theory', so the  US involvement in Southeast Asia was driven by the idea that the falling of one country to communism would result in surrounding countries  eventually falling to communism as well.

hello it is $0 for apex