Slavery was common. Disease was more common.
The Medieval Warm Period served to help boost the population back towards pre-Dark Ages levels.
That was followed by the Little Ice Age.
Now, for the major piece of history. King Arthur is reported to have booted the lords of the manor off a prime piece of property located around what we would today call Wessex, Essex, East Wessex, and West Essex (it was a communally held vast estate). He then gave the property away to the Illegal Aliens then arriving from across the Channel and mucking everything up.
Anyway, they moved to Brittany and Merlin replanted the vinyards in that country (which was far larger in those days).
Later, the whole family (thousands of people) moved further East to the headwaters of the Rhone where again Merlin directed the planting of vast numbers of vines.
Over the years this region saw the development of its own Arthurian legends.
Eventually one of the eldest daughters of a principal family married the Count of Bourbon and the rest is history.
That's the only Western European family history, with associated bric a brac, that's managed to cross over from several months before the arrival of the Dark Ages down to the end of the Middle of the Middle Ages.
Just about all the details about anybody, or even large family groups, got burned in the hearth as people attempted to avoid freezing to death in 536 and 537AD.
Even the Franks didn't keep a continuous record. They tried, but they just couldn't make it. I can only imagine they were reduced to eating their horses.
Things were rough back then!