This post has been updated.

Another Sunday sermon, another international uproar. Controversy appears to be becoming a habit for Pope Francis. A week after he accused the world of “standing mute” while Christians were slaughtered, the pope again stirred anger by calling the 1915 killings of up to 1.5 million Armenians by Turks a “genocide,” and not just any genocide but “the first genocide of the 20th century.”

He spoke during a Sunday mass at St. Peter’s Basilica to commemorate the 100th anniversary of the tragedy. “Bishops and priests, religious, women and men, the elderly and even defenseless children and the infirm were murdered.”

Turkey reacted furiously, recalling its ambassador to the Vatican and accusing the pope of spreading “hatred and animosity” with “unfounded allegations.”

Yet, the pope’s remarks weren’t exactly unprecedented. Pope John Paul II said nearly the same thing in 2001, and Francis himself made almost identical comments before becoming pontiff in 2013.

Outrage in Turkey over the “G” word — with reference to the killings that started to unfold in April 1915 amid the chaos of World War I — is nothing new. But experts say the latest furor has as much to do with current events — especially politics inside Turkey — as it does with any lasting debate over early-20th-century history.

In fact, Pope Francis is just the latest in a long line of religious and political leaders to wrestle with what has become one of the world’s most sensitive struggles over nomenclature. American presidents from Ronald Reagan to Barack Obama have walked a tightrope between the weight of historical evidence on one side, and the importance of ties to Turkey on the other. And Turkey itself has been torn over the issue of whether to call the killings “genocide,” with public figures thrown into prison or forced to flee from the country simply for uttering the word.

“It’s become hugely politicized,” says Eugene Rogan, director of Oxford University’s Middle East Center and the author of an acclaimed new book about the fall of the Ottomans. “Turkey is a NATO ally and the Turkish government responds very negatively to anybody raising the question of genocide. So it’s in that context that the furor over the pope’s comments should be viewed.”

“In order to understand Turkey and its denialism, you have to compare it to apartheid in South Africa,” says Taner Akçam, a Turkish professor of history at Clark University. “If Turkey wants to play an important role in the political development in the Middle East, Turkey has to face its own history.”

“No other historical issue causes such anguish in Washington,” Thomas de Waal wrote recently in an article titled “The G-Word: The Armenian Massacre and the Politics of Genocide” in Foreign Affairs. “Over the years, the debate has come to center on a single word, ‘genocide,’ a term that has acquired such power that some refuse to utter it aloud, calling it ‘the G-word’ instead. For most Armenians, it seems that no other label could possibly describe the suffering of their people. For the Turkish government, almost any other word would be acceptable.”

A century ago, there was little doubt about the magnitude of the massacre, de Waal writes. In 1914, the quickly crumbling Ottoman Empire sought to recoup some of its recently lost territories by siding with Germany against Russia. Turkish leader Mehmed Talat Pasha “accused Christian Armenians — a population of almost two million, most of whom lived in what is now eastern Turkey — of sympathizing with Russia and thus representing a potential fifth column,” according to de Waal. “Talat ordered the deportation of almost the entire people to the arid deserts of Syria. In the process, at least half of the men were killed by Turkish security forces or marauding Kurdish tribesmen. Women and children survived in greater numbers but endured appalling depredation, abductions, and rape on the long marches. ”

“They were essentially death marches,” Rogan tells The Washington Post. Their goal was to decimate the Armenians and prevent them from attaining “a critical demographic mass that might seek independence.”

“That was the logic behind the genocide,” he says. “Then the question was, ‘Who is going to do it?’ because massacring hundreds of thousands of people is horrible, violent work. There is documentation to show that the Ottoman government released prisoners, convicted murderers and created gangs to actually do the butchery. They also sent around propaganda to suggest that the killing of Armenians was part of the overall jihad effort that the sultan had declared at the time of the declaration of war, so that people would essentially be doing religious work in participating in this massacre.”

For decades, the world was too busy with other bloodshed. “The horrors of World War II overtook the horrors of World War I,” Rogan says.

But when the Armenian massacre was mentioned, it was never referred to as “genocide” for an even simpler reason: The word simply didn’t exist.

It wasn’t until after World War II that a Polish-born Jewish lawyer named Raphael Lemkin essentially invented the phrase.

“When Raphael Lemkin was devising the arguments around a new crime called ‘genocide’ after the Jewish holocaust in World War II, he really took the Armenian genocide as his prior example to base the concept on,” Rogan says. “Because of the scale of killing, because of the [Turkish] government’s involvement in how to do this … so it was very much with the Armenian genocide in mind that Lemkin coined the phrase ‘genocide.'”

“Lemkin had a morally courageous vision: to get the concept of genocide enshrined in international law,” de Waal writes. “His tireless lobbying soon paid off: In 1948, just four years after he invented the term, the United Nations adopted the Genocide Convention, a treaty that made the act an international crime.”

But bickering and politicking over the term began almost immediately. “In his uncompromising pursuit of his goal, Lemkin allowed the term ‘genocide’ to be bent by other political agendas,” de Waal writes. “He opposed the Universal Declaration of Human Rights, adopted a week after the Genocide Convention, fearing that it would distract the international community from preventing future genocides—the goal that he thought should surpass all others in importance. And he won the Soviet Union’s backing for the convention after ‘political groups’ were excluded from the classes of people it protected.”

America’s stance on the issue was clear — at least at first. In 1951, the United States called the Armenian killings genocide before the International Court of Justice, de Waal writes. And three decades later, Reagan referred to the “genocide of the Armenians” during a Holocaust remembrance speech.

But global politics forced Reagan to reconsider. A series of attacks by Armenian militants — including the 1982 assassination of Kemal Arikan, the Turkish consul general to the United States, in Los Angeles — prompted the president to drop all references to the “genocide.” Turkey was, and still is, an important ally, after all.

A subsequent State Department report titled, “Armenian Terrorism: A Profile,” described the events in 1915 as “ambiguous,” de Waal writes. “The Department of State does not endorse allegations that the Turkish government committed a genocide against the Armenian people,” the report said. “Armenian terrorists use this allegation to justify in part their continuing attacks on Turkish diplomats and installations.”

“From that point on, a new line had been drawn by the executive branch, and the term ‘Armenian genocide’ was outlawed in the White House,” according to de Waal.

Every American president since then has tiptoed around the issue. Before taking office, Obama had no problem calling the 1915 massacre “genocide.” Since his election, however, the president has used another term — Meds Yeghern, or “Great Catastrophe” in Armenian — to describe the death or disappearance of as many as 1.5 million Armenians, a hedging that has drawn rebukes from Armenian American groups.

Part of the problem dates back to the fuzzy definition of the word. Article 2 of the U.N.’s Genocide Convention defines “genocide” as “acts committed with intent to destroy, in whole or in part, a national, ethnical, racial or religious group, as such.”

Turkey claims that the killings were not a targeted campaign to exterminate Armenians but rather one part of a messy civil war. But Akçam and other Turkish scholars have recently shown that to be untrue by unearthing documents linking the government to the genocide, Rogan says.

“There are four main reasons why the Turkish state is so vehement in denying the Armenian genocide,” Akçam says. The first is a fear that admitting to genocide would unleash a flood of compensation claims against the Turkish government. “Turkey has been sitting on the wealth of these Armenians for a century,” he says. “We reestablished our republic on the wealth of two million Armenians.”

More than money, however, Turkish national identity is at stake. “To call the founding fathers murderers or thieves, this is the most difficult part,” Akçam says, contrasting Turkish reticence with the widespread American acknowledgement of the horrors of slavery or abuse of Native Americans.

In 2005, Turkey’s Nobel Prize-winning novelist, Orhan Pamuk, was charged with “public denigration of Turkish identity” for mentioning the massacre during an interview with a Swiss newspaper. He was forced to flee the country, although the charges were eventually dropped.

Another issue is fear of an “eternal debate” within Turkey. “If you start with Armenians, where are you going to end?” Akçam says, citing atrocities against Greeks, Assyrians, Jews and Alawites.

Finally, there is what Akçam calls “The Pinocchio Effect.”

“Turkey, like Pinocchio, has a very long nose,” he says. “It’s not easy to wake up one morning and say ‘Oh, we lied. We were wrong.'”

Akçam says he applauds Pope Francis for going further than his predecessors and for forcing the issue in Turkey and around the world.

“I congratulate the pope,” he says. “This a courageous movement, and I hope it will be a breakthrough.” Akçam hopes Obama will realize that the choice between morals and international politics is a false one, and that calling the Armenian massacre “genocide” will be better for Turkey and for the region.

“For decades, America has thought it’s better not to get Turkey angry, but it is so short sighted. It is so stupid,” he says. “This pope now has made a bold move.”