Three white peacemakers nervously waited for the Comanche council to decide whether they lived or died on Aug. 10, 1843.

Making amends with the western tribes was one of Sam Houston’s highest priorities at the start of his second presidency. But in the bitter aftermath of his predecessor’s ethnic-cleansing policy, bringing peace to the frontier would be almost as hard as whipping Santa Anna.

Mirabeau Lamar pursued his goal of an Indian-free Republic with a fanatical zeal that angered a...