In 1920, a group of communist and socialist students, teachers, and artisans, established the Regional Federation of Salvadoran Workers (FRTS), El Salvador's first trade union to organize rural and urban workers. One of the rural leaders of the FRTS was Farabundo Martí, who, together with Miguel Mármol, founded the Communist Party of El Salvador (PCES) in 1930. Between 1928 and 1932, Martí fought alongside Augusto César Sandino in Nicaragua against the United States' occupation of the country.
