This page contains information regarding Star Trek: Discovery, and thus may contain spoilers.
The Coalition was an alliance in the mirror universe that was comprised of Terran slave races – Andorians, Klingons, Romulans, and Tellarites – that rose to combat the tyranny of the Terran Empire in circa 2255. Captains Gabriel Lorca and Michael Burnham were aware of the threat to the Empire and feared that the Rigellians, Coridanites, and Denobulans would soon join as well.
In an alternate timeline created by the Guardian of Forever in 3189, Burnham warned Emperor Philippa Georgiou of the impending rebellion, and Georgiou used back channels to disrupt the Coalition. (DIS: "Terra Firma, Part 2")