The Showalter Alliance Coup

The Showalter Alliance Coup was a coup d'etat against The Alliance Leader, Howard Tenpenny, in 2179, a hundred years prior to ARKCON Relaunch (Part I), staged by Ebrown and Tara Showalter with help from Allison and a few select others in on it. It was direct response to Ebrown and Tara finding out about ARKCON, it's failure, and subsequent meeting with Tenpenny going south.

Prelude To The Coup
Source: Intro to Andromeda: Prologue