Arab nationalism was awakened by the break up of the Ottoman Empire. Arabs felt suppressed under centuries of Turkish rule, but their national ambitions were thwarted by the imposition of European neo-colonialism after WWI. At least the Turks were Muslim. New, mostly straight line, boundaries were drawn across the Mideast defining the modern colonial creations of Iraq, Jordan, Palestine (British), Syria and Lebanon (French). Earlier, European powers had established "protectorates" across North Africa: Egypt and the Anglo-Egyptian Sudan (British), Libya and Somalia (Italian), Algeria, Tunisia and Morocco (French).
Two other events during WWI or its aftermath with relevance to the current situation: the Balfour Declaration (1917) indicating British support for the creation of a Jewish homeland in Palestine; and the creation of the Muslim Brotherhood in Egypt in 1928.