Why did the Korean War start?

Welcome to the forum everyone.

The first discussion I want to have is people putting forward their argument for the [/b]most important[b] cause of the Korean War.
Think back through the options from the three categories:
Why Kim Il Sung felt he could act.
Why Stalin decided to support the invasion.
Why the US decided to retaliate.

Now decide either which category or which point from that category you think is most important and explain why.

I look forward to seeing your answers.

Mr Farndon

The willingness of Stalin to support North Korea in invading the South was the "most important" reason in causing the Korean conflict. Due to the USSR supplying the Koreans with military reinforcements, artillery and funding, Kim il Sung, whom already wanted a united Korea under his leadership, was given necessary means to invade the South. This publicly cemented the USSR and North Korean alliance and demonstrated to the United States "a clear sign of aggressive intent" which demanded a response from the USA. And so counter-factually, if the USSR had not got involved in the Korean conflict and supplied the North with weapons, the USA's involvement would have been made less likely, preventing the extent or exacerbation of the war. However through fear of communism and the domino-theory they supported the South Koreans, polarising the two sides and sparking the Korean War.