What caused the terrorist attacks in Paris?

The fundamental reason is that the western powers, led by the United States, forced their own so-called democratic ideas in the Middle East, which led to the riots of the people who were originally ruled there. In addition, the senior leader of IS was originally the backbone of Al Qaeda in the Iraq war. They want to establish their own territory, retaliate against western countries and demonstrate. Western countries can be said to harm others and ultimately harm themselves.