How did the Korean War begin?

Began June 25, 1950 because when the North Korean Communist army crossed the 38th Parallel and invaded non-Communist South Korea

The Korean War (1950-1953) began when the North Korean Communist army crossed the 38th Parallel and invaded non-Communist South Korea. As Kim Il-sung's North Korean army, armed with Soviet tanks, quickly overran South Korea, the United States came to South Korea's aid.