Why did Assyrian kings call themselves the rulers of 4 countries?

They called themselves that because under their rule were vast conquered territories. Once upon a time, ancient Mesopotamia (by the inhabitants themselves) was considered the center of the world. Other lands were considered parties to this world. For example, the Babylonian king Hammurabi called themselves “the storm of the four cardinal points.” We can say that the Assyrian rulers in some way borrowed this title and called themselves “kings of the four countries.”