Complex sentence: He joined younger chiefs, such as Osceola, Alligator and Wild Cat (a nephew of Micanopy) in opposing the treaty, and began to organize resistance among the Seminole warriors.
Split into simpler sentences: He joined younger chiefs, such as Osceola, Alligator and Wild Cat (a nephew of Micanopy), in opposing the treaty. They began to organize resistance among the Seminole warriors.