Apocalypse How: Several worlds have been apocalypsed in the ongoing course of galactic events.  Perhaps most notable are Laris (Tanion Wilds), whose former civilization wiped itself out with really dirty nuclear bombs; Ulijen (Cordai Gap), a planet that now has a distinct-looking bite in it where the power plant that worked by tapping solar heat using a wormhole to the sun’s interior demonstrated why it was a really bad idea to build one of those planetside; an unnamed peripheral world which suffered the bioweapon equivalent of a nuclear apocalypse; the Charnel Cluster, whose seed AI fail (see AI Is A Crapshoot, above) produced an Omnicidal Maniac that sterilized their entire multi-system polity; and most recently Litash (Dark Sea), which the Empire fed a strangelet bomb after being unimpressed by their continued Tortuga-like support for piracy In Space, thus blowing a continent-sized crater in the planet and setting the atmosphere on fire.

Which is not to count any of the many reasons why various and such Precursors and elder races aren’t around any more, but these are the main documented apocalypses.

As a general rule, though, in the modern Associated Worlds, the Ley Accords promise very bad things to anyone tossing around star-killing, planet-killing, or ecocidal weapons, because those things – stars, planets, and ecologies – are expensive.