Armenians and an overwhelming number of historians say that Turkey's rulers committed genocide, that its actions were a model for what Hitler did to the Jews. The Turks, meanwhile, say their ancestors never carried out such crimes, and that they too were victims in a world war.
Ever since, this battle over history has not only ensnared the two nations but even the White House and Congress, where resolutions officially recognizing the genocide are currently moving through the House and Senate.
But our story begins where the lives of so many Armenians ended, far from Istanbul, in the desert.
"60 Minutes" and correspondent Bob Simon took a drive into what is now Syria, to the barren wilderness, to what amounts to the largest Armenian cemetery in the world.
"As many as 450,000 Armenians died here," author Peter Balakian told Simon.
Balakian is an Armenian American who has written extensively about what happened in this desolate place.
According to Balakian, 450,000 Armenians died in this spot in the desert. "In this region called Deir Zor, it is the greatest graveyard of the Armenian Genocide," he explained.
Deir Zor is to Armenians what Auschwitz is to Jews. The most ghoulish thing about the place is that 95 years later the evidence of the massacres is everywhere.
Just a short distance from the banks of Euphrates there's a dump. It's also the site of a mass grave. It has never been excavated. All we had to do was scratch the surface of the sand to collect evidence of what had happened here.
Under the surface was evidence of bones. "It's the hill full of bones," said Dr. Haroot Kahvejian, an Armenian dentist who showed Simon around.
"Nobody bothered to dig them up until now?" Simon asked.
It was extraordinary standing on a mound where perhaps thousands of people lie entombed. There is no record of who they were or where they could have come from.
"Look at that. There are kids who know exactly where they are. They are finding them by the dozen," Simon observed.
"Evidence comes in many forms. It comes in photographs, it comes in texts and telegrams," Balakian said. "And it also comes in bones."
So just how did all these bones end up here?
In 1915, the First World War was raging and the Ottoman Empire was crumbling. The Armenians were a Christian minority who were considered infidels by the ruling Muslims -- a fifth column who sided with the enemy in the war.
The fact that they were prosperous didn't help, says Balakian, whose great uncle survived the genocide and wrote about it in a memoir Armenian Golgotha.
"Like the Jews of Europe the Armenians of the Ottoman Empire had a dominant role in commerce and trade, they were highly educated, many of them," Balakian.
And he said they were highly resented.
Asked what happened next, Balakian said, "What happens from the spring of 1915 on through the summer is a well orchestrated project of government planned arrests and deportations."