What is an endogenic and what an exogenic process when considering landslide triggering? Is it e.g. pore water pressure (endogenic) and rainfall (exogenic)? If this is the case you will hardly be able to draw a meaningful line - one causes the other.
Factor(s) responsible would be depending upon landslide/ slope failure concerned. You've to judge based on pre and post field studies, with emphasis on post field studies to arrive at a conclusion. Well, regional triggering factor would be including Seismicity and Rainfall.