Complex sentence: The Chinese government tries to maintain tight control over all organized religion, including Christianity, so the only legal Christian groups (Three-Self Patriotic Movement and Chinese Patriotic Catholic Association) are those under the Communist Party's control.
Split into simpler sentences: The Chinese government tries to maintain tight control over all organized religion, including Christianity. The only legal Christian groups, the Three-Self Patriotic Movement and the Chinese Patriotic Catholic Association, are under the Communist Party's control.