1 - His first error was following orders to drive the natives from the area.
2 - He split his forces ... And left his superior technology (Gatling guns) and ammunition supplies with a minor force.
Even splitting his forces, the outcome would have been quite different if he had the Gatling guns and ammo with the main force that encountered the enemy encampment.
3 - He failed to listen to his scouts ("military intelligence" of the time).
