This has most difficulty rewards I dont think theres all of them here but its still good information to know
Information is from this site: eiyuuwiki.wikidot.com/wiki:difficulty-bonus-items
its gone for some reason.

I reccomend conquering India first because its not that hard. Right away I managed to conquer Macedonia and Egypt afterwards which wasnt easy but nothing to drive me despair.

Russia is super hard to conquer before EU because you lose half your troops per unit. But it is fairly simple to defend conquered territories. Do not underestimate Russia if you think they only send a few troops when landing in Vladivostok because they will defend with full armies next time.

I had to conquer the rest of the map that I could before EU (So not Babylon and Uruk) and prioritize 6-8 of my troops to 5-6khp(maybe more) A healer is really good because you can just heal up from the cold. I dont think you can defeat russia before EU if you distributed your troops evenly because that happened to me and I had to restart to before I conquered Russia to prepare.

If you want to acquire a lot of money u could skip every 2 turns if ur action points are full. So if you used one action point, you can skip 3 turns before bandits attack.