Why did the United States become militarily involved in the Korean War? Describe one consequence of this decision

The main reason for the USA's military intervention in the Korean war was that of containment. The American aims was to work with its allies to contain the spread of soviet and communist Chinese power using political, economic and if necessary military pressures. Any failure of containment was potentially disastrous. According to the USA the loss of SK might well lead to a chain reaction leading to the loss of much of the rest of Asia, including Japan.