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MAINZ, Germany — When Allied troops swept through Europe and defeated the Nazi regime more than 70 years ago, they were hailed as liberators.

But new research by a German academic alleges that rape by U.S., British, French and Canadian forces was more commonplace than previously believed.

While some other experts dispute Professor Miriam Gebhardt's estimates, her claims have reignited the debate about the extent of crimes committed on both sides in the aftermath of World War II.

The issue of post-war sexual violence has been a taboo topic because many Germans did not want to downplay the country's own atrocities during the Holocaust by displaying its people as victims.

"The question of victimhood is not an either-or anymore," Gebhardt said. "We can and must continue to deal with our crimes, but we also have to deal with our victims."

"We too are considered an army of rapists"

Gebhardt estimates that nearly 900,000 Germans were raped by the Allied forces that freed her country from the Nazis in the wake of D-Day in 1944 until West Germany was declared fully sovereign in 1955.

That number is far more than previous estimates and is contested by other scholars, who challenge Gebhardt's methodology and question the accuracy of her estimates.

While some historians disagree on the numbers, eyewitness accounts and military court cases confirm that Americans committed acts of sexual violence at the end of the war.

In 1945, TIME magazine published a letter penned by an unidentified American serviceman who stated that “our own Army and the British Army ... have done their share of looting and raping ... we too are considered an army of rapists.”

Gebhardt, a professor of history and sociology at the University of Konstanz, alleges that 190,000 sexual assaults were perpetrated by U.S. troops while defeating the Nazis and in the subsequent 10 years.

Her estimates are partially based on the assumption that one child originated from every 100 cases of rape.

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Gebhardt’s research included examining police reports and interviews with German women, who were questioned by the country's post-1945 government to evaluate child care costs.

She also used so-called "invasion reports," compiled by priests in Bavaria to document the situation in their local communities.

"Two American soldiers raped a very decent girl," one Catholic priest from the Munich diocese wrote in July 1945, in a report which featured in a "The Crimes of the Liberators," a documentary which was produced by NBC News' German partner ZDF. "The soldiers entered a building at 10 p.m. and claimed they had to do a house search, but they were looking for two girls."

"I believe that she accepted the sexual assault as something that had to be expected, a consequence of the war"

The discussion about sexual assaults against German women has historically been focused on the crimes of the Soviet Red Army troops.

"This perception was in line with Nazi propaganda, which had been portraying the Russians as Asian, subhuman beings," Gebhardt said.

Prior to the fall of the Nazi regime, Hitler’s propaganda minister Josef Goebbels highlighted "the bloodlust and cruelty" of the Soviets, whom he claimed would go on a rampage through the country, raping German women.

A Parisian woman gives an American soldier a kiss during the Liberation of the French capital on Aug. 25, 1944. John Downey / AP

An often-quoted figure is that the Soviets committed between 1 and 2 million rapes after Germany was liberated. However, Gebhardt's new estimates link around 430,000 rapes to the Red Army, as well as 45,000 to British troops and 50,000 to the French.

Unlike their Red Army allies, Gebhardt said "the image of U.S. soldiers was by far better, that of affluence, freedom and democracy."

American sociologist Robert Lilly used military records and trial transcripts to put the number of rapes committed by U.S. soldiers in England, France and Germany between 1942 and 1945 at 14,000.

"Two weeks after the invasion, the first rapes occurred in France," Lilly told ZDF.

However, he isn't convinced by Gebhardt's estimates because access to official documents has become more difficult. “Twenty-five years ago, when I started, it was a very different research world," he said.

Maximiliane Saalfrank, a German a freelance journalist who has researched the subject since the early 1990s, said her grandmother was raped by an American GI in May 1945 in the Bavarian city of Landshut.

"I believe that she accepted the sexual assault as something that had to be expected, a consequence of the war, that it happened because she was the defeated," Saalfrank told NBC News.

Many victims kept silent about their ordeals because it was "a topic plagued with shame," according to Gebhardt.

Dr. Philipp Kuwert, the director of a 2008 research project on German rape victims at the University of Greifswald, thinks that the country is ready to deal with the difficult discussion.

"Amid the Shoah [Holocaust], it was unimaginable for German intellectuals to conduct research on non-Jewish Germans as victims,” he told NBC News. “And morally, it was right to first document the horrors of the Shoah. In order to look at both sides, a strong cultural maturity is needed."

However, an analysis published in Germany's weekly magazine Der Spiegel questioned the plausibility of Gebhardt’s findings.

Echoing other historians who have been skeptical of her theory, the magazine said that if the number of sexual assaults really were that high, "it is almost certain that there would be more reports on rape in the files of hospitals or health authorities, or that there would be more eyewitness reports."

But the magazine agreed that Gebhardt was correct on one point. It said: "For far too long, historical research has been dominated by the idea that rapes committed by GIs were implausible because German women wanted to jump into bed with them anyway."