The United States supported the Union of Peoples of Angola (UPA – "União dos Povos de Angola"), headed by Holden Roberto. With this support, the Congo-Léopoldville-based UPA attacked Portuguese settlers and Africans living in Angola from bases in the Congo. Many of the African farm workers living in northern Angola worked under labor contracts that required seasonal relocation of workers from the desertified Southwest and Bailundo areas of Angola. Photos of Africans killed by the UPA, which included photos of decapitated civilians, men, women and children of both white and black ethnicity, would later be displayed in the UN by Portuguese diplomats. The emergence of labor protests, attacks by newly organized guerrilla movements, and the Santa Maria hijacking by Henrique Galvão began a path to open warfare in Angola.