I'm referring to Southern Siberia of course, as opposed to the harsher Northern Territory. How did the mongols pull this off with such ease- or was it more difficult than I've been led to believe?
The Mongols and their steppe-based allies and subjects were from a climate just as harsh as that of Russia, and so were able to adequately prepare for winter camps and/or campaigning.
I would also posit that the Russian winter is a little overblown in terms of military effect. There are really only two examples of an invasion failing in winter -Napoleon and Nazi Germany - and neither holds up to scrutiny.
Napoleon suffered enormous hardship and loss of life due to the winter, but he was already retreating by the time winter set in - he was defeated by Russian scorched earth tactics and the impossibility of maintaining a supply line to friendly territory.
Hitler's Wehrmacht also suffered in the winter months, and I wouldn't go so far as to say that it played no factor in their ultimate defeat, but Germany campaigned through multiple winters in Russia being before defeated by superior tactics, weapons, and weight of numbers (not to mention, again, the huge and unwieldy supply line through Eastern Europe).
Hi, you may be interested in responses by /u/duxbelisarius and /u/krishaperkins in this previous post: