What is John Hersey's purpose in focusing on individual people rather than focusing on the entire city of Hiroshima?

In Hiroshima, published first in the New Yorker in 1946 and shortly thereafter as a book, John Hershey told the stories of people affected by the atomic bomb that was dropped on Hiroshima on August 6, 1945. Hershey interwove the stories of six people who survived the bombing--a seamstress, a Catholic priest (who was German), a factory worker, two doctors, and a Protestant minister. When Americans dropped the bomb, many people in the United States were glad that it, and the bomb that followed three days later in Nagasaki, forced the Japanese to surrender. After fighting a long war, they were relieved it was over and did not necessarily see the effects of the bombing on the civilians in Japan. By concentrating in detail on Japanese (or, in the case of the priest, German) civilians, Hershey emphasized the toll the bomb took on humans who were in its path of devastation. The description of what they endured, starting with the "noiseless flash" that occurred when the bomb was detonated, provided an account that allowed readers to empathize with their experience as fellow human beings.