The event that occurred first among the options listed is the Sand Creek Massacre, which took place on November 29, 1864.
Here’s a brief timeline of the other events for reference:
- Dawes Severalty Act: Enacted in 1887.
- Battle of Little Bighorn: Fought on June 25-26, 1876.
- Wounded Knee Massacre: Occurred on December 29, 1890.
Thus, the correct answer is the Sand Creek Massacre.