I can only address one such leader: Pope Pius IX. Sadly, his role was overblown at the time and continues to be misunderstood to this day.

You may read from time to time that the Vatican (or the papacy, depending on the source) recognized the Confederacy. Pius IX did write a letter to Jefferson Davis. In that letter, he did address Davis as the “[I]llustrious and honorable President of the Confederate States of America.” However, the full reality is not nearly so dramatic. This is the only place online that I have found the letter from Pius IX to Davis. It is a PDF, and it also comes from a less-than-stellar source. Ignore the rest of the content, just scroll down to the text if you want to read the letter. In sum, the letter is the equivalent of a form letter. It acknowledges receipt of Davis’ earlier letter, says that it would be really nice if there was peace instead of war, asserts that the pope will pray for peace, and that he will also pray that Davis will be granted grace.

That’s it.

So, why the address as “President?” Basically, the pontiff filled in the blank by looking at the signature of the original letter from Davis. With Italian unification and being a self-proclaimed “prisoner of the Vatican,” Pius IX had much greater concerns much closer to home than the Confederacy. Also, the idea that the pope would somehow back the South in the US Civil War is far-fetched, given the less than ideal way Catholics were treated in that region.