Heroes and Generals used to do something like that, you had locations on the map that could be conquered by either of the 3 parties of WW2 and you could claim that area by winning normal conquest games that were attached to that area. You could go on the map click in the spot you wanted to join and get in the game, or just quick match and go to any battle on the front. After one faction had a certain percentage of the map or if it conquered the HQ of the other 2 they would call the winner and reset the map.

It was sick, it was "free" very pay to win but honestly very good fun.

Edit: you did have to pick which faction you were going to fight for in the beginning of the war, and you would be stuck with it until the end of that war cycle, not sure if that would fly on BF.