Respuesta :
D. The North Koreans tried to invade South Korea, the US ally. to prevent the spread of communism in Korea , the US entered the war
The United States conducted military operations in Korea because D) They didn't want Communist North Korea to gain more power. The United States was an ally of South Korea so when the North Koreans tried to invade South Korea the United States set up there operations in Korea to prevent the further spread of communism in Korea. It was at this point that the United States entered the war.