The Tren resistance was composed of several groups of Tren opposed to the Galactic Empire during the Galactic Civil War. As the Tren's three colony planets voted one by one to join the Galactic Empire, their governments opposed the resistance groups and wiped many of them out. When the third and final colony, Nopsin, voted to join the Empire, the resistance groups gave up trying to agitate for the Tren to join the Alliance to Restore the Republic.
The Tren Opit-Wenbruh sympathized with the Tren resistance on Nopsin, but he never joined due to the sense of duty he felt toward the Nopsin military, of which he was a member.