Summary: Implement an experience value to represent doctrinal development over the course of time, and use this value when calculating battle results.
Presently, battle results are determined by quantity. Put simply, whoever has more soldiers, planes, tanks, and ships wins almost 100% of the time. I suggest adding a new dimension to conflict in the form of experience.
Experience would be a scaling value that rises sharply during active conflict, and decreases slowly during times of peace. The increase would represent the sort of doctrinal development that always occurs during a war, whereas the decrease would represent the natural decay of inactive military institutions (aging/retiring service members, equipment obsolescence during peacetime, etc).
Experience would be split into two factors: Defense and Offense.
-Defensive experience would give invaded nations an inherent bonus whilst defending, similar to the fortify command, but more dynamic. Defensive experience would decay far slower than offensive, representing the advantages of fighting on one's home-soil.
-Offensive experience would allow invading nations to circumvent defensive bonuses. Likewise, it would also apply to the invaded nation in the form of a counter-attack bonus (allowing weaker defenders to theoretically take on a sudden invasion from a stronger power). Offensive experience would decay fairly quickly, representing the issues of ever-changing battle tactics.
Both forms of experience would be earned in battles, with the type of experience gained be contingent on who plays what role. Meanwhile, the -amount- of experience gained would depend on the scale of the fighting. The more disproportionate the battle, the more skewed the experience. In other words, when an army of 100 soldiers clashes with an army of 1000, the weaker side will gain more experience. Defeat is the greatest teacher, after all!
This mechanism will naturally discourage nations from picking unfair fights, because every ass-kicking would strengthen the target to the point where they could present a serious threat as they grow.
Finally, experience growth slows the higher it gets, in order to prevent snowballing.
So, what are everyone's thoughts on this? Love it? Hate it?