During the first battle of the korean war in june of 1950,

a. the united nations pledged to come to the aid of north korea.
b. south koreans crossed the 38th parallel and continued into north korea.
c. the soviet union marched on south korea and captured it within days.
d. north koreans took control of the south korean capital of seoul.

After World War II Korea got divided into Northern Communist state backed by U.R.S.S. and a Southern Capitalist state supported by U.S.A.

The Korean War started on June 1950 when North Korea supported by the Soviet Union crossed the 38th Parallel and invaded South Korea.

75,000 North Korean soldiers moved across the boundary and overran South Korea; thus North Koreans took control of of Seoul; thereby (d).