I`ve started 2 games as Poland in CK2 recently. The first one I had to abandon, since the Mongols absolutely overwhelmed my little reign with their ~200k horde. The second game... I wish I knew how did it happen, but they've been much weaker from the start. Their advance was slower and when they eventually appear on my borders, they didn't even attack me. Out of curiosity I DoWed them, raised all my levies + archer's retinue + mercenaries + Holy Orders (basically I threw at them all I had) and waited. Their doomstack was down to ~70k + they raised another 40k from their conquered lands (I think, seeing as it had almost no Horse Archers). Barely, but that was a force that I could deal with, won a few battles against them and basically my Non-as-little-as-in-the-first-game-but-still-not-that-huge kingdom was the one that stopped Golden Horde. It was still a fairly close call, and if the Horde was anything as it was in my first game I`d lose badly...
A few things to consider (I think) when dealing with the Hordes:
- I've assasinated the Mongolian khan of the Golden Horde as soon as it appeared, his heir was Cuman. I`m not sure how did it help, but for some reason the GH's progress was much worse than the one of Il-Khanate (where the whole ruling dynasty is Mongolian still).
- Their doomstack doesn't suffer any attrition, but it also doesn't replenish. What means that if they have 200k big stack and go on to conquer 100 provinces before you, loosing 100 troops there, 200 there etc, it will with time get smaller and smaller.
- I think they do get a smaller stacks of troops (working under the same conditions as the main horde) for a few years after the invasion, then it stops. At that point the horde has to rely only on whatever it has left + raised from the conquered lands.
- I guess the main part of dealing with the hordes is luck really. If they target you first, I doubt there is a force that can stop them. If they reach your borders, they can still turn, if you're lucky, or go straight for you, if you're not. Overall it represent the fact that, in history, none has really ever defeated the hordes (sorry, Mamluks did in 1260, but the horde was already weakened by then).
EDIT: I should add that in the first game, Il-Khanate never moved pass 1 province, stood there for many years then just disappeared. GH on the other hand was an absolute monster.
In the second game, the Golden Horde conquered most of Rus, but was quite slow to do it. It had some civil wars, I think, so it eventually ran out of steam. Il-Khanat is scary though, it rules over Persia, whole Arabia, reached Synai, Palestine and Georgia. It converted to Shia already too (not sure if that's good or not, never really followed their progress that much as I assumed I won't have to deal with them either way).
