Firstly, the men conducting the raid were Confederate Guerillas. That is to say in simple terms: they were the pro-slavery guys fighting on the side which opposed the Union... which at that time was governed and led by its Republican Commander-in-Chief... Abraham Lincoln. The men doing the slaughtering would have been staunch advocates of an "anybody but Lincoln" platform for the 1860 election, but fortunately, there was no George Soros around at the time to bankroll it.
Given a choice, the Confederate killers would have voted for the Democrats, who compounded their disgusting display of attempted appeasement by offering up failed Union ex-General George McClelland as their 1864 presidential candidate, who was widely known for his desire to reach a peaceful accomodation with the Confederacy. Had he won, there would now be a CSA (Confederate States of America) as well as a USA. Oh, and the slaves would not have been freed.
Has anyone noticed that the Republicans are clearly once again the party of liberation while the Democrats have resumed, through their advocacy and support for the various forms of Socialism, their old role as the party of subjugation?