How NOT to take over Europe

Diplomacy doesn't work here either...it doesn't work anywhere!

You just gotta pull a Mongol's.

Force them to pay tribute to you, and if they don't you go in raid them and burn down their cities. Mongol's 101

I'm only reminded how much I don't know history

Surprised Russia got conquered though being so big and stuff.

Back then Russia was not what we think of well Russia, the Slavic culture was still in its early days becoming what we know of it today, also Russia didn't have Siberia yet they were west of the Ural mountain range at this point.

And what's more embarrassing is that it's about my history basically since I'm from Ukraine originally facepalm

Russia as a nation did not exist during the time of the Mongols. It was the Mongolian invasion that galvanised Muscovy, Novogrod and other areas to eventually unify into the Russian Empire to my knowledge. Thereafter, Russia just kept expanding eastwards into the colossal nation we know today. In response to the OP though, the issue with any long-term invasion of Russia is logistics and winter. Because historically, the Russians had a habit of just dragging you into hopeless attrition and when your poorly dressed French/German troops/tanks start freezing solid quite literally, then you're done. And let us not forget that because of how stupidly large Russia is, it makes up for the fact that in more focused conflicts such as the Crimean War, Russia lost spectacularly to the British and the French. It doesn't matter if your troops are trained better if they starve to death because your supply lines break. Conscription in Russia used to be for LIFE before reforms in the late 19th century and the vast majority of the population were serfs until then too. They were bound to the land they lived on, were the property of the local noble family and could be bought, sold and sent off to the army on a whim. So what it lacked in discipline and equipment, it made up for in manpower. Of course, there were immense issues with this system but for the longest time, it did work until the world thoroughly modernised. And even then, the Russians just changed their tune and adapted a little.