Yes, the South was Democratic.   The United States, which had been secured by the Union Army had as President, Abraham Lincoln, a Republican.  There was no way that Southern racists were going to be Republican after the Civil War, hence the KKK, Jim Crow, etc.  This lasted, the Dixiecrats, until the signing of the 1964 Civil Rights Act by then Democratic President, Lyndon Johnson.   Newly enabled, Blacks then registered heavily as Democratic.  You think the racist South was going to sit for that?  No way.  The South swung heavily into the conservative Republican party after 1964, away from those 'librul' Democrats.  Richard Nixon took advantage of that and won his Presidency appealing to those new Republicans of the South.  This is not the Republican Party of Abraham Lincoln, folks.  Lincoln would have been called a 'librul' Republican in his day.