I have an idea about how to make wars more realistic, but this feature I think should be on / off in settings. You don't have to add these feature if you don't want to add or its too hard to make them, but here is it.
So there would be a leaderboard that counts the army of a nation like it does in "size leaderboard" but it does not increase when gaining territories in war in same way as "size leaderboard" (it could be increasing always based on something like population growth or after war (ill explain that later), but in war it would decline) as it would look the same as "size leaderboard" that you can see, but it would be on different numbers. The thing how it could chance the war is by when war starts it would already determine who wins the war (if there are multiple nations on any side their army strengths will be combined when counting winner), but it could also have a small chance then that the nation(s) with smaller army would win. The winner(s) will be determined by it that if the attacking nation(s) have more powerful army they will win or if defending nation(s) have they will win (in case of draw they will sing a peace treaty). Then after determining who wins it would have a normal battle but the nation(s) who/that have been determined to win would win the war. Then after war is over the winning nations will get bigger army by this equation:
(old) military + ( occupied land from nation(s) who lost / ( military leaderboard ranking / 2 ) = (new) military.
Then updates leaderboard and then peace treaty get singed with nations getting their lands.
PS: could you add that nations sing small defensive alliances that don't start a world war to get some spice to game that there will came like 2 vs 3 nations war or something like that.
PPS: You are so underrated I don't understand why. (Sorry this is so long message)