Been trying to get back into EUIV and I'm pretty rusty. I also have a problem with my games going ahistorical. I don't know why. I started a game as the Hansa, conquered a bit of northern Germany, but when I had to chance to annex Denmark I didn't because I didn't think the Hansa should own Denmark. Well, it came back to bite me. Fighting a defensive war with Sweden against Muscovy, then Denmark attacks my vassal. In less than 2 years my entire country is conquered, by Denmark lol...
I think Japan is by far the easiest nation to play in VII. You can westernize ridiculously fast, but all your neighbours remain uncivilized for a very long time. European nations don't screw with you until the 1900s unless you get unlucky and crisis' start in Korea (which you should invade pretty much immediately to avoid Korea ending up under China or Russia). Netherlands and Spain usually end up pretty weak which means you can take their valuable colonies, then when the civil wars start in China you can carve out a few provinces that have millions of people. V2 is a hard game to conquer a lot in, but by the end of one of my Japan games (and I was by no means a "good" player when I did this), I had conquered the entire Chinese seaboard, a bunch of the high POP inner provinces, all of Korea, all of SE Asia was my satellites, allied to Britain, and was in the midst of invading the mainland USA because I had nothing better to do. Total population of almost 500 million, limitless numbers of brigades, a fleet better than just about every combined, and tens of millions sitting in the bank. Oh, and easily 1/1/1 in the rankings.
They call Japan the "tutorial island" for a reason. If you want to learn V2, Japan is a good place to start.