Like the work of the Belarussian Nobel laureate Svetlana Alexievich, Ms. di Giovanni’s book gives voice to ordinary people living through a dark time in history; and like Anthony Shadid’s powerful 2005 book, “Night Draws Near” (which recounted the aftermath of the American invasion of Iraq), it chronicles the intimate fallout that war has on women, children and families.

A longtime reporter who covered the wars in Bosnia, Chechnya and Sierra Leone, Ms. di Giovanni writes here with urgency and anguish — determined to testify to what she has witnessed because she wants “people never to forget.” Her sorrow comes through in the writing — in the book’s staccato sentences, in its flashbacks to similar scenes of suffering in the Balkans, in its helpless empathy for people she met in Syria, like the ailing woman in a hospital who begged her to take her children away to some place safe.

Most of Ms. di Giovanni’s travels in Syria, described in detail here, were in 2012, a year into the conflict. In that spring and early summer, she notes, wealthy elites in Damascus were still in denial about the war — though explosions from the shelling could be heard during pool parties at the Dama Rose Hotel. By year’s end, the country had slipped down “the rabbit-hole of war.” The government was targeting civilian neighborhoods, and in the case of Aleppo, “opposition forces had cut off nearly all supply routes.” In that city, she writes, there were two criteria for staying alive: “hiding from the regime’s barrel bombs, and finding food.”

As the war ground on, more and more foreigners were being kidnapped. Ms. di Giovanni met the young American aid worker Kayla Mueller, who was abducted in the summer of 2013 in northern Syria and held captive as a sex slave by the Islamic State before dying in a Jordanian airstrike on Feb. 6, 2015. And she draws a heartbreaking portrait here of her friend, the journalist Steven Sotloff, who would be killed by the Islamic State in 2014. “His slangy language, his Americanism,” his “kidlike curiosity,” she writes, helped her forget “the cold, the anxiety, the gnawing fear in my stomach” in Aleppo. She could not imagine that “this smiling, laughing boy, who told jokes and avidly followed the basketball scores of the Miami team he loved,” would be beheaded by the Islamic State militants he called the “bearded guys.”

Within months, Ms. di Giovanni says she saw Syria undergo a metamorphosis — one that would grow even darker in the years to come. Opposition fighters were becoming radicalized and sectarianism had grown increasingly bitter: “Syrians who called themselves Syrians a few years ago were now saying they were Alawites, Christians, Sunnis, Shias, Druze.” Leaving Aleppo, she writes, she did her best “to take photographs inside my head, pictures that I would remember, that would show a country that no longer existed.” Her testimony is contained here in this searing and necessary book.