Tribe: On Homecoming and Belonging by Sebastian Junger was a solid book about the important topic of how divided as a society we can be.
Junger writes of how these divisions typically fall away during times of great stress such as war or natural disaster as people are in it together, as a "community of sufferers." He additionally notes how the mental health of individuals also can improve during these times, with the bombing of London during WWII and more recently in Sarajevo cited as cases where people living in war zones generally weren't depressed, just resolute and living their lives. There was a collective cause, even if that cause was simply surviving.
Also covered in the book is how there's such a disconnect between modern society and combat veterans returning to it. For people who haven't served in wartime, the large majority of those here in the US, it's difficult to understand what vets went through, and veterans often don't have outlets where they can speak about their experiences, both educating others and unburdening themselves.
It's a short book, with Junger describing it an a Time Magazine interview as a screed, and interesting reading about this concept of Tribe and how many in modern society simply don't feel part of one.