Unfortunately, these parts of the book are also the dullest and most problematic. There’s a numbingly familiar quality to much of the social science research he cites. It is not exactly news that nations with large income disparities are less happy than those without them, or that group cooperation increases levels of oxytocin, the bonding hormone.

Image Credit... Patricia Wall/The New York Times

Though Mr. Junger cautions against romanticizing tribal cultures, he sometimes does exactly that, and in ways that can be annoying.

He notes, for example, that American mothers in the 1970s had a level of skin-to-skin contact with their babies that traditional societies would consider criminally low. Fair enough. I wonder, though, if he realizes that in saying this he’s crashing open the gate for every attachment-parenting demagogue out there? And that parents who actually have to go to work for a living — and therefore can’t have their babies pinned to their chests all day long for three years straight — will read these words and start to smack their heads against their desks?

But his arguments about how “detribalized” we’ve become are undeniably strong. It’s not just that our personal loyalties have shrunk to a universe the size of a teacup. (Our immediate families, maybe a few friends.) It’s that we have so little regard for what’s collectively ours. We litter. We fudge on our taxes. Medical providers defraud Medicare; bankers perform sleights of hand with the markets and destroy the commonweal.

But Mr. Junger’s most powerful — and surprising — argument is the one he makes about the military’s epidemic of post-traumatic stress disorder, which in many cases he suspects may not be PTSD at all. Why, if you think about it, would roughly 50 percent of our Iraq and Afghanistan veterans apply for permanent PTSD disability when only 10 percent of them saw combat? “The problem doesn’t seem to be trauma on the battlefield,” he concludes, “so much as re-entry into society.” And, he suggests, this problem might deserve its own diagnostic term.

If the United States were more hospitable to veterans’ needs, its returning soldiers wouldn’t be foundering. It is our failure to adapt to veterans that’s the problem, not the other way around.