Just paying army and fleet upkeep will eat up most of your income from trade, taxation, and resource extraction. If your Empire is stagnant, your armies are weak, you are against a coalition of enemies, and your trade routes are raided you will face an uphill game. In Total War: Rome II you will ultimately win or lose on the campaign map. Robb Stark had a point, you can be a brilliant field tactician but if you fail to make good on those victories you may end up losing in the end. 'I have won every battle but I am losing this war!'- The King in the North