I am reading a lot of "I waited until I had an overwhelming force..." It will take some time, but you need to get better at gauging how many units you need to win a battle, and beating the enemy with smaller groups, which increases the # of provinces you can take per turn.
It also sounds like a couple times the computer beat you with guerilla tactics of trading provinces with you until you were defeated economically. Expanding faster will help with some of that, but if you are in a situation where you have to trade provinces, make sure you're standing on the high income lands. If you are going to lose a province, jack the taxes up to 200.
It sounds like you are doing better though. I think I put 80 hours into the game before I was starting to feel confident in my abilities. It's worth it though, I enjoyed both my wins and losses.
