In the Islamic state magazine DABIQ,
http://m.clarionproject.org/factsheets-files/islamic-state-magazine-dabiq-fifteen-breaking-the-cross.pdfISIS states why it hates and fights the West:
“We hate you, first and foremost, because you are disbelievers; you reject the oneness of Allah.”
“We hate you because your secular, liberal societies permit the very things that Allah has prohibited while banning many of the things He has permitted.”
“In the case of the atheist fringe, we hate you and wage war against you because you disbelieve in the existence of your Lord and Creator.”
“We hate you for your crimes against Islam and wage war against you to punish you for your transgressions against our religion.”
“We hate you for your crimes against the Muslims; your drones and fighter jets bomb, kill, and maim our people around the world, and your puppets in the usurped lands of the Muslims oppress, torture, and wage war against anyone who calls to the truth.”
“We hate you for invading our lands and fight you to repel you and drive you out. As long as there is an inch of territory left for us to reclaim, jihad will continue to be a personal obligation on every single Muslim.”