Saltpeter is a mineral used to make gunpowder and at the beginning of the 20th century it was considered "white gold". Thousands of workers came to the north of Chile (formerly Peru) to work in their extraction. Working under an inhospitable climate, long days from sunrise to sunset, the salary was meager and payment was in tokens that could only be exchanged at the employer's store.
In 1907 the miners went into strike which ended with the killings of over 2,000 miners, including wives and children, committed by the Chilean Army in Iquique. For decades afterward there was official suppression of knowledge of the The Santa María School massacre, but in 2007 the government conducted a highly publicized commemoration of its centenary, including an official National Day of Mourning and the reinterment of the victims' remains.