Huns, Magyars, Turks , Mongols, since the fall of Rome, always the horse nomads came from the endless steppes to threaten or ravage Europe.
Except since the 1200s' not counting the Russians, who I see as a special case.
The challenge is to have Europe, (and the European Russians) successfully invaded by Central Asian hordes in anytime from...oh...1825 to 1900. POD can go all the way back to Genghis Khan, but later is better.