Complex sentence: Religious movements which expect that the second coming of Christ, will be a cataclysmic event, generally called "adventism", have arisen throughout the Christian era; but they became particularly common during and after the Protestant Reformation.
Split into simpler sentences: Religious movements which expect that the second coming of Christ as a cataclysmic event are generally called "adventism". These have arisen throughout the Christian era, but were particularly common after the Protestant Reformation.