The contentious verse from the Koran is 9:5, where followers are exhorted to 'fight' polytheists and use the sword to either force them to convert to Islam and pay a Tax or be killed. There are quite a few verses in the same vein, about 'fighting' non-believers and if they prove stubborn, to kill them. This doesn't sound to me as if 'jihad' is an 'inner struggle' but a physically violent means to eradicate people who continue to practise their religion and refuse to conform to the rules and mores of Islam. The problem is that there are also verses encouraging peace and mercy etc. However, it's the infamous 9:5 that seems to be causing fundamentalists to incite terrorism. It must be added that in the early verses, 'People of the Book' (ie Jews and Christians) might get away with merely paying a Tax to Muslim coffers.