Fear of Communism
Most of this fear came because of the ferocity and atrocities of the Cold War in which the USSR and the USA fought indirectly agaisnt the spread of communism and capitalism of the world. One of the key points of communism, is that it's supposed to be spread around. Every country needs to be communist in a true communist's eyes. So over the second half of the 20th century communism spread thought Europe and into China and Cuba. To stop this spread the USA fought a bloody war in Vietnam and tried to assist ate Fidel Castro, Cuba's dictator at the time.