This isn’t the “greatest generation” as it has come to be depicted in popular histories. But in “What Soldiers Do: Sex and the American G.I. in World War II France,” the historian Mary Louise Roberts draws on French archives, American military records, wartime propaganda and other sources to advance a provocative argument: The liberation of France was “sold” to soldiers not as a battle for freedom but as an erotic adventure among oversexed Frenchwomen, stirring up a “tsunami of male lust” that a battered and mistrustful population often saw as a second assault on its sovereignty and dignity.

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Sex was certainly on the liberators’ minds. The book cites military propaganda and press accounts depicting France as “a tremendous brothel inhabited by 40 million hedonists,” as Life magazine put it. (Sample sentences from a French phrase guide in the newspaper Stars and Stripes: “You are very pretty” and “Are your parents at home?”)

On the ground, however, the grateful kisses captured by photojournalists gave way to something less picturesque. In the National Archives in College Park, Md., Ms. Roberts found evidence — including one blurry, curling snapshot — supporting long-circulating colorful anecdotes about the Blue and Gray Corral, a brothel set up near the village of St. Renan in September 1944 by Maj. Gen. Charles H. Gerhardt, commander of the infantry division that landed at Omaha Beach, partly to counter a wave of rape accusations against G.I.’s. (It was shut down after a mere five hours.)

In France, Ms. Roberts also found a desperate letter from the mayor of Le Havre in August 1945 urging American commanders to set up brothels outside the city, to halt the “scenes contrary to decency” that overran the streets, day and night. They refused, partly, Ms. Roberts argues, out of concern that condoning prostitution would look bad to “American mothers and sweethearts,” as one soldier put it.