We have nuclear weapons capable of decimating civilisation, but it is the threat and knowledge of these weapons that can be the most effective weapon.
Put a giant mysterious do-hicky on top of your building, start spreading rumours that it is a powerful weapon, spread the word of its devastating capabilities through "survivors", and you effectively create a defence from attackers, who think twice about attacking your land. Propaganda is always a powerful weapon. Posture, with enough bravado and people think twice about attacking.
As i said, just playing devils advocate, as there doesnt appear to be a shred of historical evidence that this scenario is at all true.
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