A church destroyed by the Islamic State in Qaraqosh, Iraq, December 2016 © Chris McGrath/Getty Images

The longtime war reporter Janine di Giovanni’s powerful new book, The Vanishing (Public Affairs, $30), began, in her own words, as “a way of understanding how Christians in the Middle East, the birthplace of Christianity, have survived in the most turbulent of times.” She has devoted sections to Iraq, Gaza, Syria, and Egypt, traveling to each “to try to record for history people whose villages, cultures, and ethos would perhaps not be standing in one hundred years’ time.”

But di Giovanni’s…