The present day Republican party is no longer the party of Abraham Lincoln especially after 1964.  Do you think the South would have had anything to do with Abraham Lincoln after the Civil War let alone be in the Republican party? Hence, the South was Democratic for many years.  But, those Racist Dixiecrats, the white Democratic South, bolted from the Democratic party after President Johnson signed the Civil Rights Act of 1964.  And yes, Nixon was smart enough to take advantage of that with his Southern Strategy to get the edge to win the Presidency in 1966.