The Ewok revolution on Kashyyyk

They were being imported as pets/funny little guys by the Wookies, at best being treated like children. Finally they had enough and started fleeing into primordial woods that were too dense for the Wookies. After several raids the Wookies sent in a batallion of Ewok-catchers, underestimating their ability to build traps and willingness to clobber the Wookies over their heads once they got them to fall.

A second expedition wasn't much more successful, but there were enough deaths for the Wookies to finally send a call to C-3PO to arrange peace talks and return the Ewoks to their moon.