The title is a tad misleading.
Anyways, I've been trying to think of something that would make wars useful regardless if you lose infrastructure or not, without using anything that is currently in the game.
What I have just thought of is really quite simple however. If I'm not mistaken, cities in this game slowly grow. This would be used in the sorts of a meter. The meter goes from -25 to 25, in which every nation would start at -25. Each point below zero would add 1% to population growth(this is of course substitutable, but I wasn't sure if daily cash revenue would sound too OP), and each point above zero would give a 1% combat bonus to the troop of your choice. The four choices obviously being soldiers, tanks, ships, aircraft. You would earn points based on how many wars you fought, win or lose, in the past month. However, this does not count expired wars or wars that peace was made. The points you earn would expire after x amount of days. I haven't though of a way to balance the point system, or the amount of days after the war the points last, but I'd like to see opinions on this first.