The Free States: Black Migration to the Great Plains from 1864-1889
What would be colloquially called the "Free States" consists of the US states of Dakota, Lincoln, and Montana. Though to a lesser extent Nebraska (the push for a West Nebraska has so far been unable to get enough votes ins the state legislature) , Idaho, and Colorado could be included by approximation and the sizeable African-American minorities each state received during the "Great Migration of the 1860s-1880s.
The legacy of the Great Migration came to be during the worst times of the US Civil War, as the question of the status of millions of slaves would be fought for. The chief arbitrator of the Great Migration would be President Lincoln himself, as part of signing the US Homestead Act in 1862 but again adding the "Free Soil" Amendment in 1864 which included all African-Americans no matter their status could apply for land. Importantly to this was the aid of Frederick Douglass and Eustace Williams who laid out the foundation for the Office of Resettlement, while Douglass would put to work his great skill of oratory and organization in the halls of Washington it was Williams who pushed into the territories of the Great Plains and claiming sites for the first "Freedomvilles" that would be settlements of Free Blacks.
Williams initially rebuffed from Nebraska and Colorado territory went North and claimed several locations in the Dakota, Montana and Wyoming territories from 1864-1867, his original writ under Lincoln being accepted by his successor, President Grant. Even before his official return to Washington D.C. Black settlers were streaming westward to sites in the Dakota and Wyoming territories. By 1870 it is estimated some 200,000 Blacks settled in the Great Plains territories, by 1875 this number had increased to over one million. Common factors during this time for why the African Americans left the South are generally laid at discrimination faced by resurgent Confederates in the Reconstruction period, but also a economic pull as gold rushes drew settlers.
The Black settlers of course were not the only inhabitants, facing conflict in particular with the Native tribes of the Dakotas and Wyoming territories. As well as White settlers, some European but in particular Southern settlers who moved into Nebraska, Colorado and Montana and tried to enact Jim Crow laws that ultimately failed in Montana.
Dakota was the first to be admitted to the US as a state, in 1876 alongside Colorado. It would take another decade but eventually in 1889 the states of Montana and Lincoln would both be admitted into the Union with Black majorities and having no Jim Crow laws. Idaho was also admitted the same year but while not having a Black majority it certainly did not include any Jim Crow laws that disenfranchised the Black minority. Since their acceptance as states Dakota, Montana and Lilcoln would consistently elect to Congress Black senators and congressmen who would fight for equal Civil Rights for all people of color remaining in the South and other states of the Union.