Ok, I just bought a little small history on the Russian geographical era (It kind of takes the USSR borders as the limit of the study, but extended back a few thousand years)
Anyway it was to my surprise that the Slavic people of one of the khanates invited the Varingian nobility to rule them since they were largely running amok with no central strength from the khan or somesuch.
Now I knew the Irish had invited a Danish King to take the High Kingship in maybe the first century or so after Norman invasion, and the Normans themselves were descended from up North and the Byz had their Varingian guard.

My question is this, was this pretty common? Specifically requests for Northern nobility to take positioins of power in other lands? But all the rest aswell.