 Complete the following phrase:  Under colonial law, black Angolans were forbidden from forming political parties or labour unions. The first nationalist movements did not take root until after World War II, spearheaded by a largely Westernised and Portuguese-speaking urban class, which included many mestiços. During the early 1960s they were joined by other associations stemming from ad hoc labour activism in the rural workforce. Portugals refusal to address increasing Angolan demands for self-determination provoked an armed conflict, which erupted in 1961 with the Baixa de Cassanje revolt and gradually evolved into a protracted 