During and after the Serpa Pinto and Capelo expeditions, the Portuguese government attempted bilateral negotiations with Britain. In 1879 as part of talks on a treaty on the freedom of navigation on the Congo and Zambezi rivers and the development of trade in those river basins, Portugal formally claimed the area south and east of the Ruo River (the present southeastern border of Malawi). The 1879 treaty was never ratified, and in 1882 Portugal occupied the lower Shire River valley as far as the Ruo, after which its government again asked Britain to accept this territorial claim, without success. Further bilateral negotiations led to a draft treaty in February 1884, which would have included British recognition of Portuguese sovereignty over the mouth of the Congo in exchange for freedom of navigation on the Congo and Zambezi rivers, but the Berlin Conference of 1884–85 ended these discussions which could have led to British recognition of Portuguese influence stretching across the continent. Portugal's efforts to establish a corridor of influence between Angola and Mozambique without gaining full political control were hampered by one of the articles in the General Act of the Berlin Conference requiring effective occupation of areas claimed rather than relying on historical claims based on early discovery or more recent claims based largely on exploration, as Portugal wished to use.