Before 400 CE, Japan was ruled by hundreds of different clans. These clans were often led by powerful families who controlled different regions of Japan. The leaders of these clans were known as chieftains or clan heads, and they often engaged in warfare with each other to expand their territories and gain power. The clans were not united under a single government, and there was no central authority that could enforce laws or maintain order throughout Japan. This period of Japanese history is known as the Kofun period, and it lasted from around 250 CE to 538 CE.