In which french colony was the united states motivated to intervene in its war for independence because the independence movement was led by communists? philippines siam (thailand) algeria indochina

The First Indochina War, from 1946-1954, was a war of independence fought by Vietnamese Communists against the French Colonial regime.  This war lead directly to the US involvement in what became known as the Vietnam War.

So the correct answer is Indochina.