Why did Kim Il-Sung invade South Korea in 1950?

Kim Il-Sung invaded South Korea on June 25, 1950, primarily to reunify the Korean Peninsula under communist rule.12

Following the division of Korea into Soviet-occupied and U.S.-occupied zones after World War II, both the Republic of Korea and the Democratic People’s Republic of Korea were established in 1948, with each government claiming to be the sole legitimate authority over the entire peninsula. By 1950, ongoing border violence and political tensions convinced Kim Il-Sung that a war, conducted under Soviet auspices, was necessary to achieve reunification by force. Kim received support for this objective from Soviet leader Joseph Stalin and later from Chinese leader Mao Zedong.3124