Final answer:
The US got involved in the Korean War due to fears of communism spreading and concerns about defending allies. The US saw North Korea's invasion of South Korea as a threat and wanted to protect its strategic interests in the region.
Step-by-step explanation:
The reasons for US involvement in the Korean War were primarily driven by fears of the spread of communism and concerns about US credibility in defending allies against communist aggression. After World War II, Korea was divided into North and South, with the northern part falling under Soviet control and the southern part under US control. When North Korea invaded South Korea in 1950, the US saw it as a threat to its credibility in standing up against communism and a potential domino effect in Asia. Additionally, the US wanted to protect its strategic interests in the region, particularly Japan. These factors led to the US joining the conflict and providing military support to South Korea.