Who formed a personal military to fight the native Americans?

In the 19th century, various figures, including some U.S. military officers and settlers, formed personal militias to confront Native American tribes. One notable example is John C. Frémont, who led expeditions in the West and, during the California Gold Rush, engaged in military actions against Native Americans. These personal militias often operated outside official military structures, reflecting the tensions between settlers and indigenous populations during westward expansion.