Simplify the following text for a Grade 9 native English-speaking person.
Original: Goryeo united the Later Three Kingdoms of Korea ( Later Baekje , Later Goguryeo , and Silla ) and by 1374 ruled most of the Korean peninsula until it was removed by the Joseon dynasty in 1392 .
Simplified: It united the Later Three Kingdoms in 936 and ruled most of the Korean peninsula until it was removed by the Joseon dynasty in 1392 .