> Curiously, the mega-settlements of the Trypillia culture suddenly disappear from the archaeological record around 5400 years ago. In fact, populations decrease all across Northern Europe to such an extent that the period has become known in the field as the Neolithic Decline. Recent DNA evidence has suggested a possible answer: Yersinia pestis.

I've recently watched a documentary about those "proto-villages" found (... to be bigger than initially thought) in Moldova but the hypothesis for their decline was else (still according to the doc.): the theory was that at some point they just became too big to function as a whole. Initially when the size was reasonable there was also a kind of "proto-democracy" that worked naturally but that did not scale, and when the settlements became bigger that cohesion did not work anymore and people left.

That being said, the theory of a plague also makes sense, the more the people the more the chance to spread it.