A) The US military attacked North Korean forces to prevent them from conquering all of Korea.
Explanation:
At the time of the Korean War, the American government was focused on stopping the spread of communism. This policy was known as containment. This is why the US got involved in the Korean War.
At this time, North Korea was a communist country that invaded South Korea (a capitalist/democratic nation). The goal of the North Korean army was to unite Korea under one communist system.
The US did not want communist to spread, so they intervened and helped the South Korean military.
