His post:

But at that time the idealogies of the 2 parties were switched from what we know them as today. During the 1860s, Republicans, who dominated northern states, orchestrated an ambitious expansion of federal power, helping to fund the transcontinental railroad, the state university system and the settlement of the West by homesteaders, and instating a national currency and protective tariff. Democrats, who dominated the South, opposed these measures. After the Civil War, Republicans passed laws that granted protections for African Americans and advanced social justice; again, Democrats largely opposed these expansions of power.

Democrats didn’t take on civil rights as a party platform until the late 1940s. As the Democratic Party expanded its civil rights interests over the next two decades, southern democrats briefly split into the Dixiecrats and later drifted into the Republican Party. There’s an interesting Wikipedia page about the Dixiecrats here: https://en.wikipedia.org/wiki/Dixiecrat