claim had expired because they had left the area unoccupied for too long. Portugal reoccupied the ports of Cabinda and Ambriz in 1855, and relations with Great Britain improved after that. The dispute set a precedent, however, that effective occupation was a prerequisite for recognition of colonial claims. The question continued to reappear until 1885 when it was enshrined in the agreements that emanated from the Congress of Berlin. The final straw was the Anglo-Portuguese Treaty signed on February 26, 1884. It granted exclusive navigation rights on the Congo River to Britain in exchange for British guarantees of Portugal's control of the coast at the mouth of the Congo River. Most significantly, it prevented the French from taking advantage of treaties signed by one of its explorers (Pierre Savorgnan de Brazza) with Africans living along the north side of the Congo River. International protests forced the two countries to abandon the treaty in June 1884, and Bismarck used the controversy to call the Congress of Berlin later that year. The Portuguese were the first Europeans to claim territory in sub-Saharan Africa, and their example inspired imitation from other European powers. For the British, the Portuguese were acceptable proxies in the competition with France, Russia and Germany for world domination. For Portuguese governments, the British alliance gave them influence that they could not command themselves, while the idea of a Portuguese empire offered something with which to distract domestic opponents from the struggles initiated by the Napoleonic Wars. The issues that were raised by Portugal's claims in Africa and the efforts of other countries to whittle them down became the fundamental issues of the Congress of Berlin. In the end, the Congress settled more than the future of Portugal's African holdings—it also set the rules for any European government which wished to establish an empire in Africa. In the 1950s, after World War II, several African territories became independent from their European rulers, but the oldest Europe-ruled territories, those ruled by Portugal, were rebranded "Overseas Provinces" from the former designation as Portuguese colonies. This was a firm effort of Portugal's authorities to preserve its old African possessions abroad and refuse any claims of independence. This was followed by a wave of strong economic and social developments in all Portuguese Africa, in particular the overseas provinces of Angola and Mozambique. By the 1960s, several organisations were founded to support independence's claims of