A theme of John Hersey's Hiroshima is the theme of community strength and support. The bomb tore apart everything. Obviously it destroyed buildings and homes, but it also destroyed families. Some families were completely wiped out, some were completely saved. Many lost parts of their family. So after the bomb went off and survivors had to look for help, their family was not around, leaving fellow survivors in the community. Evidence from the novel can be found in what Hersey does NOT write about. There is very little narration about actual whole family units. But there is narration about people coming together in parks to provide medical aid, food, etc. to each other. It's almost like the community is the new family unit.
A second theme is the strength of the Japanese people, both physically and emotionally. The reader is brought through horror upon horror of physically destroyed bodies and severe injuries. Yet despite all of that, very little wailing and moaning occurs from the injured. Very little, if any, complaining happens. It's a cultural attitude that the people do not want to call personal attention to their needs. Father Kleinsorge comments on it in chapter two this way: “. . . the silence in the grove by the river, where hundreds of gruesomely wounded suffered together . . ."