The Fighters: Americans in Combat in Afghanistan and Iraq. By C.J. Chivers. Simon & Schuster; 374 pages; $28 and £20.

“WE’RE here because we’re here. We’re here because another unit came here and set up, and we replaced them, and no one knows what else to do.” Such was Specialist Robert Soto’s summation of America’s military strategy in the Korengal Valley in Afghanistan—otherwise known as “The Valley of Death”.

Specialist Soto had decided to enlist as a child, when he saw the rubble at Ground Zero in New York. As an FNG (“fucking new guy”) in the Korengal Valley in 2008, life was a far cry from the rhetoric of politicians and strategies of generals. The Taliban could hardly shoot straight. Yet America was not winning.

Some 2m Americans have served in Iraq and Afghanistan since 9/11. C.J. Chivers, a former marine and Pulitzer-winning war correspondent for the New York Times, has done as much as any journalist to record and understand those conflicts. In “The Fighters” he picks six individuals to portray the young fighting men who mostly remain unknown to their compatriots.

Readers should not expect an explanation of the complex, violent forces America unleashed in the Muslim world. The enemies are faceless, the wars’ overseers nebulous, distant figures (Mr Chivers regards the grunts as better judges of military conditions). Nevertheless, these intimate sketches amount to an indictment. For all their bravery, ordinary fighters had little hope of turning official policy into reality on the ground. They were victims of the failures and follies of their superiors; most who served “suffered wounds—physical, psychological, moral, or all three.”

All too often, those sent out to hunt al-Qaeda, the Taliban and America’s other foes became the hunted. The Pentagon built an archipelago of bases consisting of wooden shacks behind blast walls, but the need to supply them offered perfect opportunities for ambush. The wizardry of drones and night-vision equipment was usually no match for the intelligence the insurgents could gather from countless ordinary eyes. Firepower counted for little against the enemy’s ability to time strikes, then quietly melt away.

The catchwords of counter-insurgency doctrine—“protect the population”—sounded noble in field manuals. But what if the population did not want America’s protection? And how could the grunts possibly win hearts and minds when they spoke no Arabic or Pushtu? The doctrine appeared to work during the surge in Iraq in 2007-08, but Mr Chivers attributes that success mostly to other factors. In short, the military experts in Washington “managed, again and again, to make war look like a bad idea”.

The pen-portrait format sometimes creates a jagged narrative. And Mr Chivers offers disappointingly little insight into how things might have been done better, or whether the wars should have been fought at all. But he superbly explains how small units fight, and the impossible gambles young officers must take: send men to search for hidden bombs down “ambush alley” and risk being shot by snipers, or drive through and risk being blown up.

He captures the idealism of volunteers, the exhilaration of killing the enemy for the first time, the comradeship of men under arms, the agony of loved ones at home and the disorientation of returning to civilian life. His stories are by turn stomach-churning (a marine medic tries to gather his splintered jaw and teeth after being shot in the face) and tender (the girlfriend of one traumatised special-forces soldier throws herself on top of him as he whimpers during a thunderstorm).

These wars, Mr Chivers notes, “seemed to have no off button”. When the fighting seems purposeless, why do the servicemen keep going? To stay alive and, above all, to keep their buddies alive: “They looked after themselves, platoon by platoon, squad by squad, truck crew by truck crew, each marine having the other’s back, and staying wide of the higher-ups.”