Various responses have led me to think about what nations are willing to do in the last extremity, when they see doom impending. Over the Cold War, now apparently forgotten, major nations seemed willing to take the enemy down with them, more or less completely. Thousands of nuclear weapons can do that.
You don’t always get the chance – if the front collapses and the enemy is suddenly at the gates, a state may be beaten before it really knows what’s happening [ France 1940 ]. It’s more the sort of thing that happens in a long war. When you have time to think, and despair.
A state may reach deep down into its socks and find ways to fight back. After Cannae, Rome raised another army, fought defensively, and waited for something to turn up. The Byzantines picked up Greek fire from a refugee Syrian alchemist. I suspect that the Soviets used tularemia at Stalingrad in 1942, but many seem to think that the natural default hypothesis is that Stalin would never have done such a thing. Churchill was ready with anthrax if the Germany ever managed to cross the channel.
Sometimes desperation means taking measures that seem perfectly practical to us, but strike at the heart of the state’s ideology. Very late in the game (too late), the Confederacy decided to raise black troops – but if they were good soldiers, the whole theory of the Confederacy was wrong. Which is one more example showing the folly of being a ‘proposition nation’. Heraclius paid for his war against Chosroes by melting down all the gold and silver in the churches – not an easy thing to do in the Age of Faith. In WWII, Stalin made major concessions to Russian nationalism, the peasantry, and the Orthodox Church – sure, he was more Communist than the Pope, but hey, better pink than dead.
Sometimes a remnant retreats to the hills and continues to fight: ‘Thought shall be the harder, heart the keener, courage the more, as our might lessens.’ Usually they lose. But, sometimes, they eventually win – like Covadonga.
Sometimes a state takes the path of radical reorganization – Byzantine themes Alfred the Great and the burhs.