Complex sentence: Being predominantly political in nature, Liberal Catholicism was distinct from the contemporary theological movement of Modernism, and is distinct also both from the attitude of Catholics who are described as theologically "progressive" or "liberal".
Split into simpler sentences: Being predominantly political in nature, Liberal Catholicism was distinct from the contemporary theological movement of Modernism. It is also distinct from both the attitude of Catholics who are described as theologically "progressive" or "liberal".