For an easy world conquest the most important thing to do is to blitz the 1 city minors before they juice up into multiple stack mode (not sure how they have the cash to do that). Larger nations are a walk over since even though they have multiple cities their armies are roughly the same size as the miinors but spread out to cover more ground. Hell the hardest targets for WC is prolly the NA tribes (cuz you cant generate enough manpower to take it out quick unless you're the UK) and India since you have to transport your armies over there and soldiers sucking up upkeep while in transit would really bite in the early game.

Sad to say but i like keeping the minors hanging around to use em for target practice. I pounce on their little stacks (anywhere from 2-10) cuz their capital is already crammed full of troops, and build up some crazy kill counts for the xp.

Man getting to 5 chevrons is such a huge pain i've 4 chevrons units killings hundreds of dudes per battle and not gaining the next bar