British people living in the Shire Highlands probably encouraged the Makololo to attack Serpa Pinto, resulting in a minor battle between Pinto’s Portuguese troops and the Makololo on 8 November 1889 near the Shire River. Although Serpa Pinto had previously acted with caution, he then crossed the Ruo into what is now Malawi. When Pinto occupied much Makololo territory, Johnston's vice-consul John Buchanan accused Portugal of ignoring British interests in this area and declared a British protectorate over the Shire Highlands in December 1889, despite contrary instructions. Shortly after this, Johnston declared a further protectorate over the area to the west of Lake Nyasa, also contrary to his instructions, although both protectorates were later endorsed by the Foreign Office. These actions formed the background to an Anglo-Portuguese crisis in which a British refusal of arbitration was followed by the 1890 British Ultimatum.