The Neolithic population crash in northern Europe occurred from about 3300BC to 2900BC. By that time, cities and sophisticated civilisations had already arisen in places such as Egypt and Mesopotamia. [emphasis added]

I will recommend a good book that I'm currently reading: 1177 B.C.: The Year Civilization Collapsed

It's largely about the possibility of The Sea Peoples as the primary force for multiple civilizational collapses, but the author does a pretty good job of pointing out how little or no evidence really exists in many of the cases discussed. It's giving me a lot more perspective about the type of cultural sharing that was going on around the Mediterranean at that time.