President Richard Nixon tried to become friendlier with the USSR.
Nixon announced that the USA would not make any more military commitments. Its allies would have to take care of their own security.
The theory was questioned - communism had spread to China in 1949, to Korea in the early 1950s and to Vietnam in the 1950s.
Laos and Cambodia had also become communist, but it did not spread into the rest of South-East Asia.
So communism may have spread to neighbouring countries but this outcome was not guaranteed.