Korea had been under Japanese occupation during WWII – after Japan had lost the Allied forces and the Soviets agreed to divide Korea along the 38th parallel
Most Koreans wanted unification
The Soviets occupied the North, and the US occupied the South
The US created the Republic of Korea (ROK) in the South under Syngman Rhee
In response the Democratic People’s Republic of Korea (DPRK) was founded in the North under Communist leader Kim Il-Sung
North Korea wanted to expand its borders and communism into the south
North Korea with support from the USSR and People’s Republic of China invaded South Korea on June 25, 1950