Sentence:  The documents in this report reveal how such doctrinal disagreements have historically driven wedges within the upper echelons of al-Qa'ida. It is this intra-movement contention that comprises the soft <WSD>underbelly</WSD> of violent jihad, which can be exploited to great ends. 
Meaning of the word marked with <WSD> tags:  The side which is not normally seen, normally a dark, immoral place.