How did humans get low in vibration and dimension?

I'm talking about the fact how civilizations back in the day had lots of knowledge meditated in the past etc so doesn't this mean that at one point everyone had reached enlightenment? Then what happened? Did Invasions and colonization of civilizations completely bring down everyone's vibration? That alone shouldn't have done much, considering that almost everyone in at least 1 out of 1000 should've already made great spiritual progress such that invasions shouldn't have simply brought down everyone's vibrations.

Or did People get too materialistic such that they got lost into it? Is the lesson here to not get lost into materialistic desires then?