Dark Command (1940)

When transplanted Texan Bob Seton arrives in Lawrence, Kansas he finds much to like about the place, especially Mary McCloud, daughter of the local banker. Politics is in the air however. It's just prior to the civil war and there is already a sharp division in the Territory as to whether it will remain slave-free. When he gets the opportunity to run for marshal, Seton finds himself running against the respected local schoolteacher, William Cantrell. Not is what it seems however. While acting as the upstanding citizen in public, Cantrell is dangerously ambitious and is prepared to do anything to make his mark, and his fortune, on the Territory. When he loses the race for marshal, he forms a group of raiders who run guns into the territory and rob and terrorize settlers throughout the territory. Eventually donning Confederate uniforms, it is left to Seton and the good citizens of Lawrence to face Cantrell and his raiders in one final clash.

Unfortunately the movie Dark Command is not yet available on HBO Max.