It was 48 years ago when the Olympic Games were last held in Latin America. And like the upcoming Rio Olympics, political unrest served as an overture to the opera that was the Mexico City Olympics.

The Rio Games commence in only a little more than 2 months from now. President of Brazil, Dilma Rousseff, is in the midst of impeachment proceedings, which has sparked protests both for and against the embattled leader. However, protests against the government appear to be far greater than those supporting the government.

As the New York Times recently put it, “more demonstrators have hit the Brazilians streets than the rest of the world combined.” And the Olympics are the spark:

The Olympics will provide activists of all political stripes with another prime opportunity to voice their grievances, but this time beneath the hot glare of the global media spotlight. The Olympics raise a raft of reasons to dissent: displacement (some 77,000 people and counting), militarization of public space (85,000 security officials will flood Rio, more than double the number in London), flawed spending priorities (billions spent on Olympics while hospitals are shuttered).

So far, thankfully, little violence has come of the protests in Rio de Janeiro. But in the summer of 1968, protests against the Mexico government were considered such a threat that the President decided to end it, or face the humiliation of open government opposition at a time when the international community was expecting a stable, united and enthusiastically positive Mexico. But in actuality, Mexico City was a few sparks away from a conflagration.

Then President of Mexico Gustavo Diaz Ordaz

The first spark was on July 22, when rival student gangs in competing vocational schools got into a rumble that resulted in riots. The government shut down the riots when police invaded one of the vocational schools, assaulting students and teachers alike, somewhat indiscriminately. The attack by the police on the vocational students led to a growing solidarity of a large number of students in Mexico City. This student movement gained momentum as they raised money, distributed leaflets and held demonstrations in protest of Mexico’s President Gustavo Diaz Ordaz.

On August 1, the rector of the National Autonomous University of Mexico (UNAM), Barros Sierra, led a peaceful demonstration of 50,000 students against what were thought of as repressive actions by the government. After weeks of continued protests, the Mexican Army took over the UNAM campus – the second spark. Rector Sierra resigned on September 23, only 19 days before the start of the Mexico City Games.

The third spark came on October 2, 10 days before the world would focus its attention on the release of thousands of doves, representing peace, and the march of over 5,500 athletes from 112 nations coming together with a promise to compete as members of a united humanity. Only fifteen miles from the Olympic Village, around 10,000 university and high school students gathered in the Plaza de las Tres Culturas to listen to anti-government speeches, and to protest. President Ordaz had had enough.

At 5pm that day, the Plaza was encircled by tanks on the ground, and covered in the air by helicopters. When the helicopters sent flares into the sky, undercover troops called the Battalion Olympia, who were identifiable to the Army by the single white glove they wore, swept through the crowd. Shots rang out and people collapsed.

Richard Hoffer wrote about what later became known as the Tlatelolco Massacre, in his book, Something in the Air: American Passion and Defiance in the 1968 Mexico City Olympics. Hoffer explained that the CIA’s Mexico City station chief was relaying to Washington DC what his contacts in the Mexico government were telling him – that “the first shots were fired by the students”, and that “this was a premeditated encounter provoked by the students.” Hoffer went on to explain that was far from the truth, which has only been revealed in dribs and drabs as classified information became declassified over the decades.

In fact, according to accounts that would unfold over the years, as documents would continue to be declassified, it was murder. It was an outright massacre. It was genocide. The death toll among students and the neighbors that joined them was not 4 as the government announced, was not 8 as Scott first telegrammed, and it wasn’t 20 as the New York Times reported at first, or even 39 as it wrote a week later. It may have been as high as 325, thousands more disappearing into prisons, some of them for years.

Mexico City in 1968 is not Rio de Janeiro in 2016.

This time, the whole world is watching.