1. On May 12, 1864, a battle between the United States Army and the Sioux Indian tribe took place near the present-day town of Carter in eastern Montana. Known as the Battle of Killdeer Mountain, it resulted in a decisive victory for the Sioux.

2. The infamous outlaw Henry Plummer was hanged on May 12, 1864, in Bannack, Montana. Plummer was the sheriff of Bannack and was accused of being the leader of a gang of road agents, who robbed and killed travelers in the area.

3. On May 12, 1876, a group of Crow Indians led by Chief Plenty Coups saved the lives of two white men who were attacked by a band of Sioux warriors. The incident helped to strengthen the relationship between the Crows and white settlers in the area.

4. The city of Great Falls, Montana, was officially incorporated on May 12, 1888. Located near the Missouri River, Great Falls became a major industrial center in the late 19th and early 20th centuries, thanks to the construction of several hydroelectric dams.

5. In 1937, the first-ever official rodeo of the Montana High School Association was held on May 12 in Helena, Montana. The event featured competitions in bareback riding, steer wrestling, calf roping, and team roping, among others. Today, high school rodeo remains a popular sport in Montana and other western states.