Researchers at Rensselaer Polytechnic Institute have found that when just 10% of the population holds an unshakable belief, their belief will always be adopted by the majority of the society. This is a fact well-known to marketers and propagandists. Likewise, to conquer France or Europe, all ISIS needs is a small dedicated army that is brutal with a support of 10% of France/Europe population. The 7th century Arab invaders that ISIS is trying to emulate managed to defeat the Byzantine and Persian armies in the Middle East that were 10 times bigger than them because they were more brutal. So it is not impossible for ISIS to conquer Europe in our lifetime. Do not underestimate ISIS the way Byzantine Empire & Persia did. The only thing necessary for the triumph of evil is for good men to do nothing.
According to a poll conducted by ICM Research for the Russian news agency Rossiya Segodnya,15% of French people support ISIS terrorists. 7% of those surveyed in United Kingdom support ISIS, and 2% of the respondents in Germany sided with ISIS.