this crusade, this war on terrorism is going to take a while...,

NYTimes |  President Obama personally added a reference to the Crusades in his speech this week at the National Prayer Breakfast, aides said, hoping to add context and nuance to his condemnation of Islamic terrorists by noting that people also “committed terrible deeds in the name of Christ.”

But by purposely drawing the fraught historical comparison on Thursday, Mr. Obama ignited a firestorm on television and social media about the validity of his observations and the roots of religious conflicts that raged more than 800 years ago.

On Twitter, amateur historians angrily accused Mr. Obama of refusing to acknowledge Muslim aggression that preceded the Crusades. Others criticized him for drawing simplistic analogies across centuries. Many suggested that the president was reaching for ways to excuse or minimize the recent atrocities committed by Islamic extremists.

“I’m not surprised, I guess,” said Thomas Asbridge, a medieval historian and director of the Center for the Study of Islam and the West at the University of London. “Any use of the word ‘Crusade’ has to be made with great caution. It is the most highly charged word you can use in the context of the Middle East.”