Explanation: Upset about settlers flooding their territry, the Sioux attacked them to try to force the settlers out of their area. This resulted in a confrontation with the government.
After the start of the Civil War, the Federal government withdrew most Regular Army units from its Western outposts to the East, leaving the frontier virtually undefended. Minnesota, home of the Santee Sioux, had been relatively quiet for several years despite the fact that by 1861 about 200,000 whites had moved into the state. With the withdrawal of the army, the Sioux had expected the white influx to cease, but when settlers and immigrants continued to pour into the area despite the Civil War, the Sioux decided it was an opportunity to attack. Led by Chief Little Crow, in the summer of 1862, they raided up and down the Minnesota River Valley, killing more than 800 whites. For protection, refugees from the raids poured into Fort Ridgely, which Little Crow attacked on August 20 and 22nd with about 800 men, but failed to capture. He then attacked New Ulm, a German settlement a few miles down the valley, but the poorly armed settlers successfully defended themselves and drove off the Sioux.
Learning of the uprising, Minnesota's governor commisioned Henry H. Sibley a colonel in the state militia, with orders to quell the uprising. Sibley assembled about 1,400 volunteers, who would have normally been sent east to fight, and on September 18th, they moved up the valley after the marauding Sioux. At the Battle of Wood Lake on the 23rd, Little Crow was decisively defeated and, rather than surrender, fled to Dakota with many of his followers, thus ending the uprising. Sibley captured about 1,500 Sioux, who were tried before a military court that sentenced 307 to die. President Lincoln pardoned all but 38, who were publicly hanged in December, resulting in a temporary peace with the proud Sioux, who would attack the following spring.