In 1854 Montgomery bought land near present-day Mound City, Kansas. There, he became a leader of local Free-state men and was a strong abolitionist. In 1857 he organized and led a "Self-Protective Company", using it to move pro-slavery people out of the area. Fights with other pro-slavery people led territorial governor James W. Denver to send U.S. Army soldiers in to restore order. Montgomery sometimes worked with the abolitionist John Brown and thought about doing a raid to rescue Brown after his capture in Virginia, but snow in Pennsylvania upset his plan.