Complex sentence: He attended the 1832 Pierre's Hole rendezvous while working for the Rocky Mountain Fur Company, and fought in the bloodiest non-military battle preceding the Plains Indian wars that began in 1854.
Split into simpler sentences: He attended the 1832 Pierre's Hole rendezvous while working for the Rocky Mountain Fur Company. There he fought in the bloodiest non-military conflict that preceded the Plains Indian wars, which began in 1854.