The Worst Things You've Done to a Planet
Figured I'd open a fun topic to discussion: What is the worst thing you or the players at your table have ever done, deliberately or by accident, which has collectively harmed an entire planet?
Ours is probably a recent Mercenary campaign. We were contracted by the Duchess of Regina to do counter-insurgency against some Fremen-style rebels on Yori. The Fifth Frontier War had recently erupted and we were supposed to keep open the crucial mines which fed Regina's shipyards.
Well after finally making some headway against the rebels, we started getting multiple confirmed reports from incoming traders that the Imperial front had collapsed, Regina was under siege, and a Zhodani fleet was likely in jumpspace towards Yori.
After weighing options, we went for scorched earth.
We cut a deal with the Sultan, the local Imperial noble, to evacuate himself, his treasury, and his household and escort them back to Imperial lines in exchange for his cooperation. With that secured, we went to town. We spiked every major mine on the planet, then cut a deal with the rebels we'd been fighting to arm them and start an uprising amongst the thousands of their kinsmen working as forced labor in the mines, then blew the rail lines and depots. We left a dozen volunteers from our intel unit behind to go to ground in the population and hinder the Zhodani occupation as best they could. With all that in place and the planet descending into smouldering anarchy behind us, we dusted off with the Sultan, his harem, and an entire treasury in gold.
Our GM later informed us that he'd expected and intended for us to run out into the desert and wage a guerilla war. Nope. Screw that. We decided to make Space Taliban.