As the Prussians, dispensing with puny border nations is pretty easy. Get a big army, crush the enemy capital defenders in a pitched battle, and walk on through to victory. Shouldn't take more than a few turns, especially when you get fire-by-rank and the enemy is still in the Stone Age.
But what about the more protracted wars? They aren't necessarily wars of annihilation because the enemy capital is far, far away. Say as the Turks, you want to get Poland off your back and stop them from raiding, but you don't have the huge manpower reserves or money to take their cities. Is it worth while to cripple their local economy and take over all the industry and agriculture? Just burn everything that's not defended? Maybe force them to talk that way? Or should I just slug it out with all the raiding armies that keep popping up.