Purity Of Essence (POE) are a militant anarchist group who manage to cause the end of human civilisation (through nuclear holocaust) in several of the parallel universes explored in Robert Anton Wilson's Schrodinger's Cat Trilogy. They send a letter to the US government stating that they have placed small nuclear devices high up on most of the landmark buildings of all major US cities, and that unless their demands (including the dismantling of centralized government and the even redistribution of all monetary wealth) are met, they will detonate them. They also add that in the event of the capture of any of their number, the bombs will also be detonated.
This novel was published in 1979, decades before Fight Club and POE's actions are far more intelligent and weird than the simplistic anti-establishment violence of Project Mayhem. The POE nuclear scenario now seems incredibly unlikely given the level of security that most skyscrapers are bound to have after September 11th, as does the existence of non-religious extremist groups willing and able to go to such lengths. But hey, you don't have to believe it to enjoy the book. There's a lot more to it than its plot, as with all of Wilson's books.