Royal Navy to enforce their ban on the slave trade. This coincided with a series of renewed military expeditions into the bush. By the mid-nineteenth century Portugal had established its dominion as far north as the Congo River and as far south as Mossâmedes. Until the late 1880s, Portugal entertained proposals to link Angola with its colony in Mozambique but was blocked by British and Belgian opposition. In this period, the Portuguese came up against different forms of armed resistance from various peoples in Angola. The Berlin Conference in 1884–1885 set the colony's borders, delineating the boundaries of Portuguese claims in Angola, although many details were unresolved until the 1920s. Trade between Portugal and its African territories rapidly increased as a result of protective tariffs, leading to increased development, and a wave of new Portuguese immigrants. Between 1939 and 1943 the Portuguese army carried out operations against the nomadic Mucubal people, accused of rebellion, which led to the death of half their population. The survivors were incarcerated in concentration camps, sent to forced labor camps, where the great majority of them perished due to the brutality of the work system, undernourishment and executions. Angolan independence 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. Portugal's 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 war of independence that persisted for the next twelve years. Throughout the conflict, three militant nationalist movements with their own partisan guerrilla wings emerged from the fighting between the Portuguese government and local forces, supported to varying degrees by the Portuguese Communist Party. The National Front for the Liberation of Angola (FNLA) recruited from Bakongo refugees in Zaire. Benefiting from particularly favourable political circumstances in Léopoldville, and especially from a common border with Zaire, Angolan political exiles were able to build up a power base among a large expatriate community from related families, clans, and traditions. People on both sides of the border spoke mutually intelligible dialects and enjoyed shared ties to the historical Kingdom of