Artificial war delaying, or as I like to call it, suicidal lemming mentality.
Contrary to what the name of the trope might suggest, it does not imply that the country is run by a cabal of crazy militarists (and even if it is, that is irrelevant, because the population supports its government to the bitter end and even after). Even also, losing the war NOT means the extermination of the loser.
It usually comes in three complementary variants:
-Citizens of a country, whether civilian or military, are rabid fanatics who will support the continuation of the war (which they started, or were willing to break out and doing everything possible to make it break out.) This they will do even if the odds are so brutally against him that it's not even funny. This means that even if they are defeated in battle, they will regroup in the shadows and constantly attack as partisans.
-Normally it is the same country, but the government/military of one of the belligerents will try to prolong the war as long as possible because they trust that, if they prolong it long enough, something will happen that will completely turn the situation around.
Normally it is a mystical arcane such as "without a doubt my enemy's economy will collapse and that will allow me to force an end to the war on my terms" or "without a doubt the neutral countries will jump to my aid because due to the balance of powers It isn't in their interest that this one crushes me too much" or "if I drag out the war long enough, I will link it with the next great war and therefore I will have the support of one of the belligerent sides.
-One of the countries will prolong the war because it is trying to force the unconditional surrender of the other. This means repeatedly rejecting offers of negotiated peace, both from his own people and from the enemy, because he is hell-bent on forcing unconditional surrender.
Basically the assumption that the whole world will treat all wars as if they were existential conflicts that admit no other outcome than total victory or total annihilation.