The nearly one-minute video showed members of the Islamic State in Nigeria “slashing the throats of 10 people and shooting an additional person,” reported the New York Times. The ISIS group claimed that the murders were in retaliation for the earlier deaths of two radical Islamic leaders, Abu Bakr al-Baghdadi, the ISIS caliph killed during a U.S.-led raid in Syria in October, and Abu al-Hassan al-Muhajir, another ISIS leader killed the next day.

“This message is to the Christians in the world,” a man’s voice said on the video, speaking in both Arabic and Hausa, a Nigerian dialect. “Those who you see in front of us are Christians, and we will shed their blood as revenge for the two dignified ...