Why Da'esh hit Paris
Da'esh is what we have been calling ISIS or ISIL, but here's a rundown of why Da'esh is a much better term for them. Their goals include establishing a worldwide Caliphate, an Islamic state governed (in Da'esh's model) according to the most primitive and brutal principles that vaguely resemble anything the typical 21st century Muslim would recognize. Their long-term goal is immanentizing the Eschaton, or triggering Armageddon.
So, other than general hatred of things Western and secular, why would they hit Paris? France, like the US, is possessed of a significant segment of society with a deep mistrust of all Muslims, especially recent arrivals from the Mid-East. Despite the fact that a typical recent arrival seeking refugee status was most likely motivated to leave home and undertake that perilous journey specifically to get away from Da'esh's violence and repression. They may have been specifically identified by Da'esh as enemies. They arrive on our shores with the potential to be the most effective enemies of Da'esh.
But how can we help Da'esh? Start mistreating all Muslims who live within our borders, and especially any who have just arrived as refugees from Da'esh areas. Make sure to reinforce the Da'esh's propaganda that the West is hostile to all things and all people Islamic. Refuse to treat refugees' situations as a serious threat to them, rather treat the existence of all Muslim and/or brown people as a serious threat to White society.
This will probably suffice to recruit thousands of able-bodied Muslims to the cause of Da'esh, and boost their manpower greatly in order to ensure that the next operations will be more extensive and more successful.