Victory is not always an option, but defeat always is.
I regularly hear "War never solves anything." (I work in Madison, what do you expect?) Sometimes it does, of course, but by and large it is true that war doesn't solve problems. But the slogan is an exercise in missing the point. So what if it doesn't solve problem X? That doesn't mean it isn't necessary sometimes. The lawn doesn't stay mowed, the flu isn't defeated forever, and in this fallen world there are people who now and then will try to kill you--and sweet persuasion doesn't work with all of them--or even most of them. And fighting back doesn't always come to any conclusion beyond "Not this time."
Pundits warn us that "Israel didn't win in Gaza(*)" and "Israel can't win in Gaza". I suppose pundits don't get paid if they don't say something everyday, but it isn't exactly a surprise that wars are generally inconclusive. (Maybe to those whose knowledge of history is from cartoon books...) If you succeed in exterminating your enemies, that's generally a complete win (except for the bit about losing your own soul), but generally sides are well enough matched that there's a return bout a few decades down the road. "We taught them a lesson in 1918, and they've hardly bothered us since then."
Of course the aftermath of a war is critical too. The US won the first and second Iraq campaigns, and then helped win the first revolt, but under Bush we bobbled the reconstruction and then we elected a president who gets bored quickly with responsibility and dropped the ball completely. And so we lose--and so do a lot of other people. It isn't fair to them, but a lot of things happen to us because of what other people decide--good and bad--no matter whether we deserve them or not.
(*) What is it about Gaza and not Syria or the Assyrian Christians or Yazidis--no riots in the streets on their behalf and they're getting hit harder.