Poor hunting grounds remained for the Sioux Indians after they ceded lands east of the Red and Big Sioux Rivers in Minnesota and Iowa; they became increasingly hostile to white settlers and traders, many of whom encroached on Indian territory and were unscrupulous in their dealings. Suddenly, in August 1862, a band of Sioux warriors under Chief Little Crow (1803?-1863) ambushed and destroyed an army detachment from Fort Ridgely on the upper Minnesota River and then besieged the fort itself; whites were massacred at New Ulm, Minnesota, when the Sioux attacked the settlement on August 24, 1862. Minnesota's Governor Henry H. Sibley (1811-91) raised a volunteer militia force at Fort Snelling and set out to punish the Sioux, who had created panic by their barn burnings, slaughter of men, women and children, and destruction of crops. At Wood Lake in what is now North Dakota, Sibley decisively defeated Little Crow (September 23, 1862), who excapted westward but returned the next year and was shot dead by a Minnesota farmer. Earlier, 307 captive Indians were sentenced to death; most had their sentences commuted, but 38 were hanged on December 26, 1862, in the largest mass execution in US history. Meanwhile, a large military operation was begun by Sibley in cooperation with General Alfred Sully (1821-79). Sibley and his men were victorious against Sioux bands in North Dakota (July 1863), and Sully was, too, in a simultaneous but separate campaign. The latter led another expedition that marched into the Badlands and crushed a large Sioux force at Killdeer Mountain (July 28, 1864); it then swept westward to the Yellowstone River, killing those of the Sioux who decided to stand and fight, before returning to the newly established Fort Rice near present-day Bismark, North Dakota.