I'm tempted just to fly through the campaign on normal mode.
I chose hard mode, and I've been trying hard mode and it seems if I go clear some enemies out up north, I get hit from the south. Then I try going south to react to the attacks and I get hit in the north.
Income is only good enough for one 20 stacks army (and some battles are close calls). What are the tricks to getting through that campaign on hard mode? Am I supposed to be bouncing back and forth? Should I be building walls in hard mode? Should I not be expanding really quickly? If so, how long do I wait? Or maybe I'm supposed to ensure I always have a certain amount of income not being spent on my army?