In 2376, the Neo-Purists detonated electromagnetic pulse bombs across the planetary surface of Trill that killed off a great many joined Symbionts, including much of the Trill Senate. The next day, the President of Trill ordered a moratorium on all future joinings, as nearly 90% of the Symbionts had died in the attacks. (DS9 - Worlds of Deep Space Nine novel: Trill: Unjoined)