Isolate them from the rest of the world. Make them feel part of a special elite group, with an important mission.
"Monuments and historical landmarks will someday be erected to commemorate us, and our sacrifices."
Tighten your group's bond by establishing scapegoats and enemies. Demonize outsiders as less than human, biased, corrupt, or conspiring against the group. Develop an "us versus them" mentality.