WASHINGTON—Most of the reviews of Clint Eastwood’s “Flags of Our Fathers” salute the movie as a powerful work of art whose message is that war, whether of choice or necessity, is always horrific.

Actually, it does a lot more than that. It tells us that war tends to involve a double act of predation: the one each warring side inflicts on the other and the one the government—and that vast latticework of interests hidden under the guise of patriotism—inflicts on those who do the fighting and on the rest of society back home.

The first kind of predation is blatant and easily understood, even if it means a country is ready to pay a high price in order to achieve a worthy goal. The other type is more subtle: It is not measured in corpses, it does not take place on the battlefield and it blurs the borderline that separates good and evil. In that respect, war can compromise the moral rectitude even of those who fight for the good cause.

The film, based on James Bradley’s book of the same title, focuses on the men who raised a flag atop Mount Suribachi, the highest mountain on Iwo Jima, on the fifth day of the American assault on the Japanese island in 1945. The picture taken by an Associated Press photographer who has no inkling of the events that will be triggered by his camera is quickly seized upon by the American establishment and becomes a powerful propaganda tool at home. The three surviving raisers of the flag are enlisted as the patriotic symbols of a war-bond drive the government conducts in order to continue to fund its efforts.

There is fraud and deceit at every stage. The flag raised in the picture is not the original flag but a replacement ordered by a commander eager to keep the real one; none of the three survivors of the picture paraded by the government around the nation are real heroes nor do they see themselves as such—they were taken out of the battlefield long before the conclusion of the struggle so they could participate in the propaganda campaign; and, finally, one of the men named in the picture was not really there. The fact that he was one of the men who raised the original flag—the one that was not photographed—only serves to stress the theatrical nature of the ploy.

Individuals that they are, the three surviving Marines deal in unique and different ways with the collective farce they are asked to set in motion in order to bring the nation under the patriotic spell. One is happy to go along with the lie, but eventually realizes the very people who fete him are unwilling to give him a hand once the fervor of the war passes; the other is driven to drink and then death by the psychological torture of what he has seen on and off the battlefield; the third one survives—unhappy, guilty, repressed—to eventually help his own son, the author of “Flags of Our Fathers,” tell the story.

Clint Eastwood’s genius consists of rendering an equally poignant and disturbing picture of the two wars—the relentless savagery going on in the battlefield, where American and Japanese soldiers are engaged in primeval brutality that resulted in 27,000 deaths, and the damage that those conducting the politics of the conflict inflict on the truth back home by bamboozling the public into the perception that war is a beautiful expression of nationhood. In the civilian war that runs parallel to the military war, the crushing machinery of power grinds the psychologies and inner lives of real individuals in the interest of the state’s pursuits. But the damage goes beyond the soldiers forced to strut on the propaganda stage: To the extent that the ploy legitimizes deceit, it tends to blur the difference between justice and injustice, slowly eroding the moral foundation of the war that is being fought.

This, Eastwood seems to tell us, is what usually happens in war. If it happened in the struggle against Japan, Germany and Italy in the 1940s, is any war safe from moral degradation on both sides? “Flags of Our Fathers” does not seek to deny that World War II was a necessary war. It does something much more important than that by telling us that all wars, including what some would call wars of necessity, compromise the decency of the good guys as well as that of the bad guys. That is something every commander in chief with the power to unleash war should bear in mind.