Answer:
ISIS attacked Paris in 2015 in response to Operation Chammal, carried out by French military against jihadist cells in Iraq and Syria.
Explanation:
Operation Chammal is the name of the military operation that France carries out in Iraq to contain the expansion of the Islamic State, in support of the Iraqi Army, since September 2014. The operation is limited to air attacks; French President François Hollande has reiterated that ground troops will not be used.
On November 14, 2015, ISIS claimed that the Paris attacks of the previous day were a reprisal for Operation Chammal.
