Looking for good war game for PC - strategy, not FPS?

I'm looking for a good strategic war game -- something like the old Panzer General. Either turn-based or real time is fine. In particular, I'd like something from WW2 era, or even Civil War or Napoleanic era. Would prefer a game that could be played head to head with a friend through the internet. I'm not interested in fantasy games. It's been so long since I've been in the game market I just don't know what's available any more. Many thanks.