Question

Why were North and South Korea divided after World War II?

Answer 1

As a result of Yalta Conference and the surrender of Japan in WW2.

Explanation:

After the Yalta Conference, the Soviet Union declared war on Japan on August 8, 1945 and their troops landed Korea on August 13.
The US became anxious that the USSR might occupy the whole Korea. So, the US proposed the division of Korean Peninsula along the 38th parallel north, and it is agreed by the USSR.

https://en.wikipedia.org/wiki/Division_of_Korea

Japan surrenderd on August 15, 1945 and the Republic of Korea(South Korea) was founded on the same day. Democratic People's Republic of Korea(North Korea) was founded on September 9.

Answer 2

The end of World War 2 was very confused in Asia. Russia and the USA planned to split much of the Japanese occupied land before the Russian attack began.

Explanation:

The Soviets (Russians) had not fought the Japanese since 1939. The Japanese experience in 1939 wasn't good and they decline to fight the Soviets for most of World War 2. The Soviet–Japanese Neutrality Pact was signed in 1941.

Near War's end The Russians had agreed to enter the War against the Japanese 3 months after the end of the war with Germany.

The Soviet attack started on August 9, 1945. The Soviets invaded Manchuria and Korea. The Soviets advanced to the 38th Parallel in Korea (approximately the present day border) and stopped, as had been agreed with the USA previously, even though there were no US occupation forces in Southern Korea only Japanese. The US soon occupied the area south of the 38th Parallel. After a short attempt to reestablish a Japanese colonial government the US decided to create a Korean one. As time passed and the Cold War began the Soviets and the USA sponsored competing governments in Korea.

The American chose Syngman Rhee as leader. The Soviets chose Kim Il-sung. Kim had aspirations to unite Korea. (So did Syngman Rhee) The Chinese Civil War had wrapped up in 1950 with the Communists in charge of Mainland China. While the Communists were on a roll, Kim Il Sung amassed the armed forces necessary to attack the South. He asked permission from Stalin and Mao to invade the South and he did so on in June 1950 thus starting the Korean War.