Complex sentence: Chamberlain resigned the party leadership rather than act against what he believed to be his duty, and was succeeded by Bonar Law, whose views and intentions he had divined the evening before the vote at a private meeting.
Split into simpler sentences: Chamberlain resigned the party leadership rather than act against what he believed to be his duty. He was succeeded by Bonar Law, whose views and intentions he had predicted the evening before the vote at a private meeting.