 When constitutional rule was restored in 1932, a strong middle-class party, the Radicals, emerged.It became the key force in coalition governments for the next 20 years.The Seguro Obrero Massacre took place on September 5, 1938, in the midst of a heated three-way election campaign between the ultraconservative Gustavo Ross Santa María, the radical Popular Front's Pedro Aguirre Cerda, and the newly formed Popular Alliance candidate, Carlos Ibáñez del Campo.