Lewis views Christendom and Islam as civilizations that have been in perpetual collision ever since the advent of Islam in the 7th century. In a seminal essay The Roots of Muslim Rage (1990), he saw the struggle between the West and Islam gathering strength. It was in that essay that he coined the phrase "clash of civilizations", which received prominence in the eponymous book by Samuel Huntington.[8]
In 1998, Lewis read in a London-based Arabic newspaper Al-Quds Al-Arabi a declaration of war on the United States by Osama bin Laden, a person of whom Lewis had never heard before. Recognizing in bin Laden's language the ideology of jihad, Lewis wrote an essay A License to Kill in which he warned about the danger presented by the holy warrior.[8]