The Australian government were momentarily paralyzed by how quickly communism had spread internationally. Because of Vietnam's civil war, the situation caused great concern in the United States. American leaders believed in the 'domino theory'. That is the belief that if South Vietnam fell to communism, other countries in the region (Cambodia, Laos, Thailand, Malaysia and Indonesia) would also fall under the influence of communism, just like a row of dominoes. As the fear continued, the United States decided to send troops to Vietnam to support the government of South Vietnam and fight against the communists. The phrase 'domino theory' began to be used as a shorthand expression of the strategic importance of South Vietnam to the United States, as well as the need to contain the spread if communism throughout the world.