I know it's quite an open ended question, but I've always been fascinated by the fact that the Mongols conquered and ruled Russia and Ukraine for quite some time.
What were the consequences? Was there a massive demographic shift of "Asian" people into Russia/Ukraine? Did it effect political and religious issues?
It didn't change the commoner demographic makeup, but it change the makeup of the Russian nobility.
Mongol-Tatar Muslim nobles from the Golden Horde remnants converted to Orthodox Christianity, married Russian women and were given noble titles and became part of the Russian aristocracy.
The Russian noble Yusupov family were descended from a Mongol-Tatar Muslim named Yusuf who converted and married a Russian woman.
Even noble families which weren't descended from them tried forging ancestry to the Golden Horde. The Russian Aksakov family forged ancestry to the Horde.
Russian poet Derzhavin was descended from a Tatar Muslim noble who converted.
Russian nobility was of mixed blood.
As Russia incorpoated former Golden Horde territories, its peoples served in the Russian Army and Cossacks. Tatar Muslims joined Cossack hosts and Bashkirs formed special units in the Russian military.