In 1951, the Portuguese Colony of Angola became an overseas province of Portugal. In the late 1950s the National Front for the Liberation of Angola (FNLA) and the People's Movement for the Liberation of Angola (MPLA) began to organize strategies and action plans to fight Portuguese rule and the remunerated system which affected many of the native African people from the countryside, who were relocated from their homes and made to perform compulsory work, almost always unskilled hard labour, in an environment of economic boom. Organised guerrilla warfare began in 1961, the same year that a law was passed to improve the working conditions of the largely unskilled native workforce, which was demanding more rights. In 1961, the Portuguese Government indeed abolished a number of basic legal provisions which discriminated against black people, like the "Estatuto do Indigenato" (Decree-Law 43: 893 of September 6, 1961). However, the conflict, conversely known as the Colonial War or the War of Liberation, erupted in the North of the territory when UPA rebels based in Republic of the Congo massacred both white and black civilians in surprise attacks in the countryside. After visiting the United Nations, rebel leader Holden Roberto returned to Kinshasa and organised Bakongo militants.