The Huns - Scourge of Roman Europe

well, in the Hunnic army were probably also some slavic elements. Some known words of hunnic language are present in many slavic languages.

It's more likely the Slavs adopted elements of Hunnic languages when the Huns conquered them. English gained a lot of French loan-words after William the Bastard deposed the rightful king

Huns real political importance was gone in 1918. German Kaiser Army was the last stand of Huns.

whoever Huns and Mongols were, the Germans were the last to continue their politics. I would also add the Germany of Hitler despite the association with the iron cross. The symbol of cross does not translate here with  keeping up with western christian traditions.

I haven't seen any good evidence of who Huns or Mongols were. just a bunch of hogwash. The Mongols apparently were in the business of kidnapping tradesmen and dragging them to new places to build castles and cities for them. If so, the Kremlin-like structures, castles with massive walls and chess-board pattern streets surrounding cities were built during Mongol times. The place the Mongols took the craftsmen from would be, mostly, Venice and Vicenza and the so called Byzantium (note that consonants v/w and b were interchangeable in the middle ages), but not only from there. Now, the question is what became of those kidnapped people, what new ethicity did they manage to create, what new history did they write to project the roots of their culture, who they are today? Any takers?

There was no Russia back then. Russia and earlier Kievan Rus and some other EE states were formed on the ruins of mongol khagnates. Mongols had their world  color coded. This code is visible in early eastern Europe when Slavs appeared. It still does not explain who the Mongols were.
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The idea is they were Altaic speakers, but despite such military success no one speaks Turkish in Europe.  They may have been related to the Ottomans. Another is they were Magyars and what is left is modern Hungarian. They ruled in Eastern Europe for a few hundred years. They left similar building style that extends far further to the west than their putative Golden Horde lands in Russia.

Civilisation brought about by Christians was far from peaceful. The Crusades were a bloody adventure. Many people were pagans paying blood tax to whoever seized the land. Mongols controlled the whole of Eurasia, at least on the map. In reality, it was not possible in the medieval world to somehow maintain such a large state. I would look for ties with the Ottomans; however, unlike the Ottomans, the Mongols pretty much vanished from the face of history. They also left castles and burghs and cities, which is the only real thing they left. No language, no religion, no descendants, odd for the biggest empire in history. Could they have been Muslims? Orthodox eastern Christianity was in many ways and manners a crossroad between Judeo Christianity and Islam.