The journalist Sebastian Junger first heard of these defections during conversations with a much-loved surrogate uncle while growing up in a Boston suburb. Decades later, the stories form the starting point for his quest to understand why American soldiers returning from Iraq and Afghanistan are experiencing such a debilitating epidemic of post-traumatic stress disorder (PTSD).

The result is Tribe, an electrifying tapestry of history, anthropology, psychology and memoir that punctures the stereotype of the veteran as a war-damaged victim in need of salvation. Rather than asking how we can save our returning servicemen and women, Junger challenges us to take a hard look in the mirror and ask whether we can save ourselves.

The core of Junger’s argument is that many of today’s veterans owe their distress less to traumatic experiences during their deployments and more to the inevitable sense of alienation they experience on return. With its toxic politics, yawning rich-poor divide and racial tension, the US has strayed so far from the egalitarianism, self-sacrifice and solidarity that ensured the survival of our hominid ancestors that it now takes the extremes of war and disaster to spark such values back into life. “As awkward as it is to say,” Junger writes, “part of the trauma of war seems to be giving it up.”

Even for a writer with such a storied career as a war reporter, to explore the virtues that conflict can galvanise – rather than to dwell on its predictably tragic consequences – is a brave path to tread. Yet Junger never romanticises bloodshed: the book is more a critique of the corrosive impact of unbridled individualism on the economy and politics of modern America than it is an ode to war.

Tribe is a different sort of book from The Perfect Storm, Junger’s reconstruction of a doomed fishing expedition adapted into a film starring George Clooney; or War, his portrait of US soldiers at an outpost in Afghanistan, where he co-directed an Oscar-nominated documentary with his close friend Tim Hetherington, the acclaimed British photojournalist killed in Libya in 2011.

This new book is an extended essay – interspersed with brief but vivid flashes of personal recollection spanning formative years and family history as well as assignments in Bosnia, west Africa and Afghanistan. Its power lies in the breadth of detail Junger has marshalled and the quiet anger that fuels his prose. “Modern society has perfected the art of making people not feel necessary,” he writes. “It’s time for that to end.”

While he is by no means naive about the hardships and cruelties of archaic societies, he argues that the banding together that was an imperative for our forebears is integral to living well. Modernity, for all its technological miracles, has delivered some of the highest rates of depression, anxiety and loneliness in history. Members of the Kung tribe in southern Africa would never have tolerated the equivalent of hoarding food – the parallel Junger draws is with the obscene bonuses of Wall Street.

Historical examples support his contention that crises rekindle an ancient, more organic way of relating to one another. During the London blitz, planners projected that up to four million civilians might have breakdowns – in the event, psychiatric admissions fell and strangers formed self-organising communities in bomb shelters. In Northern Ireland, suicide rates dropped 50 per cent during periods of riot. Similarly, the US witnessed a two-year hiatus in mass shootings after 9/11 – with New York experiencing an immediate drop in rates of violent crime and psychiatric disturbance.

“If war were purely and absolutely bad in every single aspect and toxic in all its effects, it would probably not happen as often as it does,” Junger argues. “But in addition to all the destruction and loss of life, war also inspires ancient human virtues of courage, loyalty and self-sacrifice that can be utterly intoxicating to the people who experience them.”

While studies suggest that almost 20 per cent of US veterans of Iraq and Afghanistan have symptoms of PTSD or major depression, Junger believes that this figure does not square with the comparatively low casualty rates relative to previous wars, or the fact that only one in 10 veterans experiences actual combat.

To put the American experience in perspective, he points out that the Israel Defence Forces have, by some measures, a PTSD rate as low as 1 per cent despite decades of intermittent war. In Israel, where about half the population serves in the military, the “thank you for service” mantra breezily offered to American veterans would be as meaningless as thanking somebody for paying their taxes.

Junger is clear-eyed about the prospects that the US will rediscover a sense of solidarity anytime soon – suspecting that only a 1930s-style Depression or a catastrophic natural disaster might have the remotest chance of changing its fundamental economic logic. He reaches the bleak conclusion that the best way to attack his country would be to leave it alone – it would implode into internecine strife without an external enemy.

Despite its occasionally despairing tone, Tribe is a stirring clarion call for a return to solidarity. In advocating a public, shared confrontation with the psychic scars of war, Junger aims to stop trauma burning a hole through individual veterans. Such a collective catharsis might also be our best hope of healing the wounds modern society has inflicted on itself.