I think it would be neat to have defeat and surrender tied to political will (PW) rather than directly tied to the opposition accomplishing specific war goals. Different war acts could cause PW to decrease on the target country, and different countries might see their political will react differently to the same war act. Political will wouldn't be a global stat, but rather each war would have it's own PW calculation.
The PW surrender threshold of a war could be tied to:
1) Who is declaring war on you and how threatening they are
2) The goals of the war (perhaps these could escalate?)
3) Other wars being fought concurrently
3) Casualties and resources lost/length of war
4) Loss of key territories
5) Nature of the political establishment of the country (are they prone to win at all costs, or surrender before things get out of hand?)
6) Nuclear attack
7) Military success or failure
8) Alliance considerations (Obviously these are just a few examples that spring to mind, refinement would definitely be needed)
For instance, the smaller democratic European countries could face huge PW damage just by having war declared on them by a strong Germany, and relatively small battles could also greatly damage PW. Losing the capital would lead to almost certain immediate surrender. Countries such as Russia or China, however, might see little damage to PW despite high casualties and heavy loss of key territory when attacked by their historic enemies, necessitating truly monumental victories to defeat them. If Japan were to earnestly invade the Russian Far East in 1942 with intent to annex that territory, Russia's political will might be determined by:
1) How threatening is Japan? If Russia feels they could handle them, the PW threshold is raised. If it's more evenly matched, this might not have much of an influence
2) Has Germany invaded? If so, and it's not going great, the PW threshold is lowered, perhaps dramatically
3) High emphasis on the control of key territories sought by Japan
4) Military success or failure
5) Would Stalin allow defeat?
Basically, to Russia, curtailing the war aims of Germany is much more important than curtailing Japan's, so there is more PW to fighting Germany than Japan. If Japan has trouble taking key territories and loses a few major battles to Russia, Russia's PW to fight that war increases, and it will be harder for Japan to force Russia to cede. But if Japan captures territories and wins some major battles, and Russia is fighting Germany at the gates of Stalingrad, the Kremlin would probably be much more inclined to cede their backyard to Japan to focus on Germany at the front door, unless they are truly determined to win or go down swinging at all comers.
Say you invade France as Germany. The French stubbornly defend Paris, but you are able to take much of the rest of the country. This could lead to PW collapsing and a realistic victory without it hard-coded that you need to take Paris. Say you're the USA in mid-1945 and Japan's PW is still high. You could decide to either invade the Home Islands and blunt their PW through brutal military conquest, or you could finish production of your atomic weapons and bomb them into surrender, winning the war as historical without setting foot in Japan. Alternatively, if Japan is able to clear the Pacific of American navies, inflict high casualties, and maybe take Hawaii, America might come to terms. But then, if Japan presses their advantage and goes for the American mainland in lieu of a more equitable peace, it might lead to America's PW raising to an enormous level, turning the conflict into a true total war and fight to the finish (leaving only nukes or conquest as options for surrender).
Perhaps this would be a bitch to code, but I don't think that it's necessarily the case. Paradox does a great job of quantifying rather abstract values, so I would think it's at least a possibility (though probably not at this late stage in development). There would definitely need to be some refinement, and I'm sure there are at least a few major hurdles to clear and drawbacks to the system, but I feel there would be immense enjoyment and replayability in a system where you can win a war by using your own distinct strategy, not necessarily taking the exact same territories over and over. Skinning cats and all that. And I grant this does nothing to address the options available once a peace deal is in the works, but I feel it gets you to that stage in a more meaningful way
