Complex sentence: The 1933 Concordat between Germany and the Vatican prohibited clergy from participating in politics and in the aftermath of the Nazi takeover and signing of the Concordat, the outspoken nature of opposition by German Catholic leaders towards the Nazi movement weakened considerably.
Split into simpler sentences: The 1933 Concordat between Germany and the Vatican prohibited clergy from participating in politics. The past outspoken nature of opposition by German Catholic leaders towards Nazism weakened considerably.