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 (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.