To the right of the minimap in the upper left corner is an arrow, click on that and it will bring up an options panel.

Select autotax and automanage and auto-assign if you want the computer to do it for you.

Otherwise, you'll need to manage each province.

I like the SP campaign mode because I have ot manage each province, that's the main part of the game.

If you want to just fight the battles, but don't like the management part, try coming online and giving multiplayer a try.

ichi