What were factors that led to the Korean War?

Some factors leading to the Korean
War:

Kim Il Sung, totalitarian dictator of North Korea
(N.K.), originated the idea of invading South Korea (S.K.) and had some Russian military
advisors who were stationed in Pyongyang, draw up a plan. Kim believed that the U.S.
would not help the Rhee government in S.K. and that even if they did, he could win his
war before they arrived. He was also encouraged by the fact that there were some
communist guerrillas in S.K. who would rally to his aid when he
invaded.

In 1949, Mao of China told N.K. diplomats that he
supported N.K.’s plan for communist expansion but that he could not provide troops to
help before his Chinese communists had a secure hold of all of China. Only after N.K.
had lost its war and pleaded for help, did Mao send troops into Korea. At that, it was
more MacArthur’s strategy than pleading from Pyongyang and Moscow, that brought China
into the war. MacArthur had pushed his United Nations (U.N.) forces right up to the
Chinese border, though China had warned him not to. Chinese Manchuria bordered Korea and
was a vital industrial region of China. China was afraid that either U.N. forces would
invade Manchuria, or Russian forces would invade Manchuria in order to "protect" it from
the U.N. forces. Also, before Japan had annexed Korea, Korea had for a long time been a
loyal tributary state of China, so it would look bad if China did not come to the aid of
its fellow communist state of N.K. to repel the U.N. invaders from its
soil.

Only after a series of pleas from Kim Il Sung, did
Stalin of the U.S.S.R. give a hesitant approval for Kim’s invasion of S.K. Stalin gave
this approval after negotiating a mutual defense treaty with China in which negotiations
did not go as he had hoped. He had asked Mao for several concessions that would have
permitted some U.S.S.R. forces to remain at a few locations in China. Mao wanted China
to be completely independent of the U.S.S.R., so he refused. Stalin decided Mao was not
going to be as easy to get along with as he had hoped. Ever since the end of World War
II, N.K. had been a U.S.S.R. satellite state. Stalin now decided that a reunified Korea
under Russian influence might be a good counter-poise to China. Not only to China, but
also to the strong American presence in Japan. He figured that if Korea was reunited
under U.S.S.R. influence, the U.S. would transfer troops from Europe to Japan and he
thought this would be good for Russia (to get the U.S. troops away from U.S.S.R.’s
satellite states in Europe) and bad for China. Stalin was also optimistic because of
communist guerrillas in S.K. and because the Rhee government in S.K. had become
unpopular. The U.S.S.R. would appear weak in the eyes of the world if it did not aid its
satellite state, N.K.

The U.S. had committed itself to
helping S.K. become a nation-state. The largest number of U.S. civilian and military
advisors anywhere in the world was in S.K. U.S. policy-makers believed that a loss of
its client state of S.K., would mean a loss of U.S. prestige all around the
world.

Jo, Yunghwan. 1991. "The Soviet and Chinese Roles in
Initiating the Korean War, and Its Link to the Origins of the Sino-Soviet Dispute" in
Chullbaum Kim, ed., The Truth about the Korean War: Testimony 40 Years
Later. The Eulyoo Publishing Co., Seoul,
Korea.

Lee, Steven Hugh. 2001. The Korean
War. Longman, 33-34.