True. There were a multitude of kings, queens and kingdoms across India, but the study and spread of the cultural and literary roots of India happened all across the sub-continent.

That is why, even today, the same chants used in temples in the north, are used in the south. The text, meanings, rituals, practices, etc, may have taken a regional flavor, but the essence is the same, the core is the same and the philosophical idea behind it is the same.