I see all the memes about guillotines for the rich, funny in spirit, but actually building one in the town square is not practical. They take a ton of materials, they are huge, and they do not even work reliably. Would it not make more sense to build one from metal with hydraulic pistons or something? I am not a machinist, but a more mobile unit you could wheel into a square to decapitate a few effigies seems about as effective for sending a message, and easier to remove or relocate if needed.
Put them in jail. If you’re in a position to execute someone, then you’re in a position to imprison them. These are not supervillains who can break out of Arkham Asylum every time there needs to be a new round of villainy.
Why wouldn’t it? It freed Canada.
At these points you’re in a state of active war with another country, execution is not an option. You need to fight the actual war at that point.
Afterwards, though, once you’ve won the war and have captured the leaders and war criminals and such? No need to execute them, the war has been won. Imprison them.
Those aren’t the examples at issue, though. Unless you think a guillotine is a battlefield weapon?