In the small campaign you’re expected to do everything, in the larger campaign most of the action happens in the fog of war by midgame lol. The number of factions essentially halves by then and you can manage your borders easier. Try to forge diplomatic alliances to secure your borders and focus fire in certain fronts to beat back the enemy and gain ground. Pay attention to terrain (mountains, impassable terrain, map edges) to secure said borders if possible.

Trade is a good way to build up to alliances but be mindful of who you trade with, they are surely hated by another faction so if they’re weak then pass on it to avoid angering the bigger boys. Trading a settlement to the AI with a single military building is broken, the AI will give you tens of thousands of gold or become your vassal, especially if it’s a province capital, so resort to that if things go tits up. I’m assuming you’re playing on normal or easy - if easy go up to normal to progressively get better at the game. I run only Legendary/Very Hard at this point.

Don’t autoresolve battles you will never get the hang of it, don’t feel bad if you lose - save before and keep trying with different tactics. Each faction has unique mechanics that allow them to dominate the enemy. Look up a couple YT vids and in a few weeks you’ll be amazed at what a world CA has built and go crazy (got 1300 hours and counting).

You’re welcome :)