Earth Shattering Kaboom: The Ulijen Disaster. If you’re going to build an experimental power plant that taps power from your sun using a wormhole, don’t build it on the planetary surface!
Also, relativistic kill vehicles and really big strangelet bombs, or even antimatter bombs; and in theory, some other esoterica like twist-pinch bombs and causal weapons. All of which are utterly, utterly illegal to use (which doesn’t stop everyone with a sense of paranoia from maintaining a relativistic deterrent fleet, of course) under pain of serious obliteration.
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