TOPSHOT - Demonstrators march to the Zocalo square, in Mexico City, during the commemoration of the 50th anniversary of the 1968 Tlatelolco student massacre on October 2, 2018. - Fifty years ago, Mexican troops opened fire on student demonstrators, killing hundreds just days before Mexico City hosted the 1968 Olympics -- one of the darkest episodes in a year of global turbulence. (Photo by ALFREDO ESTRELLA / AFP)