In recent decades, the Arabic word "jihad" — once used to describe the duty of all Muslims to act according to their faith — has become overwhelmingly associated with the waging of violent war against nonbelievers. With the rise of Islamic State, another term has been refashioned for inclusion in the lexicon of extremist violence: "hijra."

As with jihad, this is no mere semantic hijacking. The real-world implications are all too alarming. By militarizing the concept of hijra, which traditionally referred to Muslims' peaceful migration to lands where they would be free from persecution, they have created a powerful tool for radicalizing and recruiting Muslims far and wide, including in the United States and Europe.

Hijra's association with Islam has its origins in the Prophet Muhammad's escape from Mecca to Medina in 622, to avoid assassination and preserve his community. He and his followers knew that as long as they remained in Mecca, they would be despised by non-Muslims; their very lives were in danger. And so, in an act of hijra — or migration — the prophet left the city of his birth. Islam would have a stable base, because Muslims in Medina would be free to worship according to the dictates of their faith.