The population of Minnesota in 1850 was only 6,000, but a treaty with the Sioux the next year opened up the fertile western region to settlement. By 1857 there were 157,000 residents, and Minnesota was admitted to the Union in 1858 as the 32nd state.

When the Civil War began, the federal government withdrew most Regular Army units from the West to be replaced by militia. The Sioux in Minnesota, angered by the cession of their lands to white settlers and delays in payments from the government, chose this time to rise against the whites. In August, 1862, Indians led by Little Crow raided up and down the Minnesota River Valley. More than 800 settlers and soldiers were killed before forces under Sibley, who had been named a colonel in the state militia, put down the uprising.