Just throwing my two cents in here, with negative thing on my idea. Make it so the country that wins in the map,
ONLY THEY have the opinion to vote for the next map. In which after the map is won, people can not join that country after the war is offically done. Now, I don't know if you can jump countries after that happens because I have never tried, but it would be the only negative thing about that idea if one can. If someone can't, then I can't think of any other negatives factors, aside from whines from people who don't like the map selected

Also, set a limit for all maps that can be voted per week so the same map isn't picked over and over again.