In the 19th century, Ashkenazi and Sephardic versions of Judaism were very different. As I mentioned in my monograph "The Novelty of Orthodoxy," some historians attribute this to long-standing differences between the two, while others attribute it to the different environments. Ashkenazi Orthodoxy developed as a response to developments in Christian Europe, for better or for worse; Sephardic Jewry, which was not faced with such developments, did not change in that way.