I'm all for naming things more precise, but functionally speaking at that point it's really just semantics, you still end up with some DB column acting as a flag, and from then on you need to take it into account in every single query that touches that table in the whole app. Since most modern ORMs know how to handle soft-delete internally, it's far easier to just stick to the defaults and use `deleted_at` if you really need a way to keep the records around. And you often need, for the referential integrity of the historical data.

You mean saving Western Europe :)

Mongols ran over (and did a lot of slaughter in) the most of Eastern and Central Europe, including Poland, Czechia, parts of todays Germany, Hungary, Bulgaria, Croatia and Austria. There was no "buffer" that stopped them, they've stopped eventually because their Great Khan died. As the leadership broke down and fights for power arose, they've been forced to return back home.

Varangians came primarily from todays Sweden, and were initially going inland into the today's Estonia, Belarus and Russia from north, from the Gulf of Finland, using rivers. The group of them called Rus under the leadership of Rurik created Novgorod in 862. About 20 years later they've also conquered Kiev (some 900km more to the south). They were initially raiders, but over time they've conquered the local Slavs, established their rule and became very important traders, as they've created the trading (and also slave) routes all across the continent from the Baltic in the North down to the Black Sea - using huge rivers like Volga and Dneper - trading in south with Byzantin empire and Abbaside Caliphate. It was one of the main trading routes between West/North Europe and Arab world of that age.

And as their presence grown stronger, the Rus started more frequently raiding the Byzantin Empire, sacking even the big Constantinople a few times. To stop these attacks, in 10th century the Byzantines did the same move as king Charles the Simple did in Francia with Normans, they gave Varangian leaders some titles and employed them all as a royal guard. Problem solved.

And then, as you've said, the viking era was over, and they assimilated into the Slavic population (just like Bulgars and others did).

Another interesting note, the Rus ethnonym also got into many Slavic languages as a word for fair blonde or reddish-blonde hair ("русая" in Russian, "rusa" in Serbian/Croatian, etc.). In Serbian 'rus' was historically used in folk language with a meaning 'red', for instance for skin rush, names of some herbs, etc.