Who: Leader of the Seminole Indians When and Where: The Seminole Indians in Florida were engaged in a bitter guerrilla war that proved to be the costliest Indian conflict.(1835-1842) Fifteen hundred American soldiers lost their lives in the battle. The war ended when the Americans captured Osceola and held him captive. Osceola eventually died in captivity. Why: Split up the Seminole tribe into the Everglades and Oklahoma. (The costliest Indian conflict) One of the many Indian conflicts that furthered westward expansion for the Americans.