Answer:
1 Korea was occupied by Japan from 1910. This meant that there was no established Korean government when Japan surrendered in 1945, though there were several pretenders.
2 Korea was divided at the 38th Parallel into Soviet and US occupation zones. This was meant to be temporary, but the Cold War freeze meant that the division became permanent. Both sides created a republic in their own image. Partition of countries usually leads to war.
3 By 1950, Soviet and US troops had withdrawn (apart from military advisers).
4 Both the DPRK and the ROK proclaimed themselves the legitimate government of all of Korea. Both favoured immediate unification by force if necessary.
5 The Communist camp did not think the USA would intervene in Korea, as they had not intervened in the Communist victory in China in 1949. In fact, no one anywhere (or hardly anyone) believed the USA would intervene.
Step-by-step explanation:
Result: civil war broke out soon after US troops had left in 1950.