I tend to think that they were "large" civilizations in central-northern europe too. I'm sorry I can't give the source right now but they were some archeologists who found in northern germany a kind of battleground that happened in the early bronze age with a lot of corpses indicating a battle of thousands of men If I recall correctly. We know that they got a lot of amber that greeks really liked. Again I cannot tell the source right now but I remember that scholars found an ancient neolithic city in the balkans, I think they estimated the city with approx 5000-10 000 souls ( I mean real archeological papers not ancient origins lol). And it leads to the environment, aegean had stones, egypt sand, mesopotamian canals and northern-central european had big big forest. So any colossal structure ( in my oponion) would be more related with woodwork. I don't see why a culture in relation with early greeks and passing knowledge wouldnt have build a big city and temples with all the ressources they got in wood and "money" made with trading.

Yes it fu ked everything during that time, a millennial(s?) of relation, trading, economy between very distanced culture. But the biggest problem is we do not have direct written knowledge/artefacts of bronze age central-northern europe, exept that there were a lot of trade routes for amber and other goods. It leads to think that maybe they were good relations between europe up-north and aegean regions. Again there's no artifact proving that they were smelting iron during that time (central-northen europeans)

God I love this subject, one of the most interesting event in ancient history. First, I remember that there's a map illustrating the sacked cities with dates that were documented and survived the centuries, like in hellas, anatolia, ugarit, levant, egypt. It seems that it started around the aegean sea, again of what we know of. There's the dorian invasion theory attached to it, that supposedly they came from the north (thrace, epirus, illyrian) or maybe farther who knows, there's an good research about DNA of early greeks very closely related to "georgians" near caucasus. Did it start with only one greedy/wary nation ? We know that the sea people were a coalition (dwelling in their islands far away on the dark sea; a approximation of what I remember a pharaon (rameses II?) said about them)