>Wipe out Belegar early
>Move on with my life
>20 turns later he rolls up with this stack
>Turns out he confederated a little dwarf faction somewhere really annoying and I didn't notice.

I realize now what makes dwarves so annoying to fight is there's no good way to fight them. Most factions can't beat them at ranged on higher diffs. You can't shut down their ranged with light cav or flyers because they're all hybrid units. They're crazy resistant to magic. All you can do is try to overwhelm them with melee spam and hope you win the grind.