The 38th parallel became an important dividing line between

Korea and China.

North and South Korea.

China and Taiwan (Formosa).

North and South China.

Verified Answer :

The correct answer is the two Koreas: South and North Korea.

The 28th parallel has been the border between them prior to the Korean War (1950-1953), which happened in the context of the Cold War, and which ended in stalemate.

After the War the border changed slightly, with North gaining a city but loosing more territory.