In 1888, the Portuguese government instructed its representatives in Portuguese East Africa to attempt to make treaties of protection with the Yao chiefs southeast of Lake Malawi and in the Shire Highlands, and an expedition organised under Antonio Cardoso, a former governor of Quelimane, set off in November 1888 for the lake. Rather later, in early 1889, a second expedition led by Alexandre de Serpa Pinto moved up the Shire valley. Between them, these two expeditions made over twenty treaties with chiefs in what is now Malawi. Serpa Pinto met Johnston in August 1889 east of the Ruo River, when Johnston advised him not to cross the river into the Shire Highlands. Previously, Serpa Pinto had acted with caution, but in September, following minor clashes between Serpa Pinto's advancing force and Kololo who had been left behind by Livingstone at the end of his Zambezi expedition in 1864 and had formed minor chieftainships, he crossed the Ruo to Chiromo, now in Malawi. In response to this incursion, Johnston's deputy John Buchanan declared a Shire Highlands Protectorate in Johnston's absence, despite the contrary Foreign Office instructions. It seems probable that Buchanan's action, made without reference to the Foreign Office, but following instructions that Johnston had left before he departed for the north, was to prevent any further advance by Serpa Pinto rather than to establish British rule in the area. However, in October 1889 Serpa Pinto's soldiers attacked one of the Kololo chiefs, killing around 70 of his followers and, with two armed river boats, pushed up the Shire River through the area over which Buchanan had established a protectorate. After Serpa Pinto's departure owing to serious illness in November 1889, his second-in-command, João Coutinho, pushed on as far as Katunga, the nearest river port to Blantyre, and some Kololo chiefs fled to Blantyre for safety.