Concessionaires holding prazo estates from the Portuguese crown were active in the lower valley of the Shire River from the 1830s and the Portuguese government claimed suzerainty over much of Central Africa, without maintaining effective occupation over more than a small part of it. In 1879, the Portuguese government formally claimed the area south and east of the Ruo River (which currently forms the southeastern border of Malawi), and in 1882 occupied the lower Shire River valley as far north as the Ruo River. The Portuguese then attempted to negotiate British acceptance of their territorial claims, but the convening of the Berlin Conference (1884) ended these bilateral discussions. Meanwhile, the African Lakes Company was attempting to obtain the status of a Chartered company from the British government, but it had not managed to do so by 1886. In 1885-86 Alexandre de Serpa Pinto undertook a Portuguese expedition which reached the Shire Highlands, but it failed make any treaties of protection with the Yao chiefs in territories west of Lake Malawi.