Even the idea that all wars are won on the basis of superior force is a bit facile, to say the least.

The Revolution is a perfect case in point. The British could have easily won it at several junctures.   But as I have noted, there was always a strong domestic element against the war--particularly in trading centers.   Interestingly enough the opposition also included several leading British generals--the Howes, for instance, at least one of whom said he would not take a command against the Americans.   Under royal pressure he reversed, but especially in the early years was torn between making war and negotiating peace.

If you send generals who are not convinced the war should be fought, you may not have a victorious outcome.

Even after Yorktown it is not at all clear that the British had been beaten by superior force--especially since the French had told the Americans 1781 was the last chance--and France was going bankrupt in large part because of costs helping the Americans. Washington recognized the tenuous nature of the situation, and pressed the French for further campaigns against Charleston and New York--without success.   It was the only the change in UK government which spelled the end of the war.

Self-interest is in fact the reason to determine when to end a war--and whether it is a victory or defeat.

And those who wanted trade with the US--and saw that as the UK's self-interest, rather than a continuing, draining, war, won out--over George III.