The violence by Muslims responding to comments by the pope fit a pattern that has been building and accelerating since 1989. Six times since then, Westerners did or said something that triggered death threats and violence in the Muslim world. Looking at them in the aggregate offers useful insights.

• 1989 – Salman Rushdie's novel, The Satanic Verses prompted Ayatollah Khomeini to issue a death edict against him and his publishers, on the grounds that the book"is against Islam, the Prophet, and the Koran." Subsequent rioting led to over 20 deaths, mostly in India.

• 1997 – The U.S. Supreme Court refused to remove a 1930s frieze showing Muhammad as lawgiver that decorates the main court chamber; the Council on American-Islamic Relations made an issue of this, leading to riots and injuries in India.

• 2002 – The American evangelical leader Jerry Falwell calls Muhammad a"terrorist," leading to church burnings and at least 10 deaths in India.

• 2005 – An incorrect story in Newsweek, reporting that American interrogators at Guantánamo Bay,"in an attempt to rattle suspects, flushed a Qur'an down a toilet," is picked up by the famous Pakistani cricketer, Imran Khan, and prompts protests around the Muslim world, leading to at least 15 deaths..

• February 2006 – The Danish newspaper Jyllands-Posten publishes twelve cartoons of Muhammad, spurring a Palestinian Arab imam in Copenhagen, Ahmed Abdel Rahman Abu Laban, to excite Muslim opinion against the Danish government. He succeeds so well, hundreds die, mostly in Nigeria.

• September 2006 – Pope Benedict XVI quotes a Byzantine emperor's views that what is new in Islam is"evil and inhuman," prompting the firebombing of churches and the murder of several Christians.

These six rounds show a near-doubling in frequency: 8 years between the first and second rounds, then 5, then 3, 1, and ½.

The first instance – Ayatollah Khomeini's edict against Mr. Rushdie – came as a complete shock, for no one had hitherto imagined that a Muslim dictator could tell a British citizen living in London what he could not write about. Seventeen years later, calls for the execution of the pope (including one at the Westminster Cathedral in London) had acquired a too-familiar quality. The outrageous had become routine, almost predictable. As Muslim sensibilities grew more excited, Western ones became more phlegmatic.

This article is reprinted with permission by Daniel Pipes. This article first appeared in the New York Sun.