Sometimes, sadly, giving up is the right thing to do.

I get it, but if you are just trying to make the point that, if a country thinks they'll eventually lose, it's better for everyone if they give up quickly ... then this historical example doesn't seem relevant.

Given that Ukraine already gave up quickly once (in Crimea) and that Russia simply waited until it was convenient to invade them again, I'm sure you can understand why Ukrainians think it's necessary to fight this one out.

Now, the war of the Triple Alliance is often held up as an example of how a minority of belligerents can create massive devastation by continuing a guerilla war after losing the conventional war; if Ukraine seems in danger of losing the conventional war, I'll admit it's a relevant parallel, otherwise it isn't terribly relevant.