The Three Kingdoms Period
Before they were kingdoms, they were nomadic Mongolian tribes. There were quite a few tribes but only 4 were able to settle down and create their own states. These 4 were Koguryo, Paekche, Silla, and Kaya. Each kingdom plus the Kaya Confederation wanted the entirety of the Korean Peninsula under their own rule. This sparked the Three Kingdoms Period, a violent era in which these four states battled for dominance over the Korean Peninsula from 57 BC to 668 CE.