The modern Democratic Party truly arose in the 1830s, with the election of Andrew Jackson.

From Wikipedia: From the end of the Civil War, African Americans almost unanimously favored the Republican Party due to its overwhelming political and more tangible efforts in achieving abolition, particularly through President Lincoln's Emancipation Proclamation. The south had long been a Democratic stronghold, favoring a state's right to legal slavery. In addition, the ranks of the fledgling Ku Klux Klan were composed almost entirely of white Democrats.

(The Republican Party was...)Founded in northern states in 1854 by anti-slavery activists, modernizers, ex-Whigs and ex-Free Soilers, the Republican Party quickly became the principal opposition to the dominant Democratic Party. It first came to power in 1860 with the election of Abraham Lincoln to the Presidency and oversaw the American Civil War and Reconstruction

Early Republican ideology was reflected in the 1856 slogan "free labor, free land, free men.

The Party had the goal of containing the expansion of slavery, which would cause the collapse of the Slave Power and the expansion of freedom.

The party took on the mission of saving the Union and destroying slavery during the American Civil War and over Reconstruction.

So bite me. The answer is that the history of the CURRENT Democratic party is one of pro-slavery, Klu Klux Klan membership and anti-union.