Southern Germany is divided into two parts, Bavaria and Baden-Württemberg. Bavaria is predominantly Catholic, Baden-Württemberg is predominantly Protestant. I say predominantly, because both have regions with the majorities of the other. Both are, however, very much more conservative than most other parts of Germany. There are many reasons for that. One is that Southern Germany was the only major region that was not under Prussian control when Germany united. They have always been extremely critical of what came from Berlin (or Bonn, for that matter), and are thus very conservative by German standards. Especially Bavaria.
However, there are other regions in Germany that are predominantly Catholic, especially the Rhine-Ruhr areas, around Cologne and Düsseldorf. And that was a problem during German unification, because a) these have always been the most populous areas of Germany, b) they were politically under Prussian control, and c) the Prussian rule had a very significant Protestant identity. So during the Bismarck years, there was a very harsh Catholic-Protestant division that was very difficult to overcome, and it was really only overcome under Wilhelm II., when German Hurrah-Patriotismus became the name of the game.