I'm now reading The Anglo-Saxons, about how the invasion of Saxons after the Roman troops left Britannica overwhelmed the Britons and it was a classic apocalyptic TSHTF end of everything: mass depopulation (they starved, fleeing the cities, no food supply), very suddenly no archeological record of pottery, or nails, or money ----- all gone. The villas became uninhabited because of no fortifications. Many hordes of coins and such have been dug up from that time because people buried their treasure and then ----- were killed.
The Saxons took over entirely.
The same thing at that same time resulted in the fall of Rome and the Dark Ages, though the invaders were different --- Goths and Huns and Vandals, mostly.
Invasions of barbarians that kill and loot and burn ARE what end societies, kill cultures.
And it is what is going on now here. The entire population of Latin America is moving north in great cavalcades, and no one stops them.