Their activity may be ascribed to the following causes.  The slave-trade has for generations been pursued in Africa.  The negro tribes themselves have long practised it; and the Arabs, in their gradual conquest of many districts of Central Africa, found it to be by far the most profitable of all pursuits.  The market was almost boundless; for since the Congress of Vienna (1815) and the Congress of Verona (1822) the Christian Powers had forbidden their subjects any longer to pursue that nefarious calling.  It is true that kidnapping of negroes went on secretly, despite all the efforts of British cruisers to capture the slavers.  It is said that the last seizure of a Portuguese schooner illicitly trading in human flesh was made off the Congo coast as late as the year 1868[463].  But the cessation of the trans-Atlantic slave-trade only served to stimulate the Arab man-hunters of Eastern Africa to greater efforts; and the rise of Mahdism quickened the demand for slaves in an unprecedented manner.  Thus, the hateful trade went on apace, threatening to devastate the Continent which explorers, missionaries, and traders were opening up.

[Footnote 463:  A.J.  Wauters, L’Etat independent du Congo, p. 52.]

The civilising and the devastating processes were certain soon to clash; and, as Stanley had foreseen, the conflict broke out on the Upper Congo.  There the slave-raiders, subsidised or led by Arabs of Zanzibar, were specially active.  Working from Ujiji and other bases, they attacked some of the expeditions sent by the Congo Free State.  Chief among the raiders was a half-caste Arab negro nick-named Tipu Tib ("The gatherer of wealth"), who by his energy and cunning had become practically the master of a great district between the Congo and Lake Tanganyika.  At first (1887-1888) the Congo Free State adopted Stanley’s suggestion of appointing Tipu Tib to be its governor of the Stanley Falls district, at a salary of L30 a month[464].  So artificial an arrangement soon broke down, and war broke out early in 1892.  The forces of the Congo Free State, led by Commandants Dhanis and Lothaire, and by Captain S.L.  Hinde, finally worsted the Arabs after two long and wearisome campaigns waged on the Upper Congo.  Into the details of the war it is impossible to enter.  The accounts of all the operations, including that of Captain Hinde[465], are written with a certain reserve; and the impression that the writers were working on behalf of civilisation and humanity is somewhat blurred by the startling admissions made by Captain Hinde in a paper read by him before the Royal Geographical Society in London, on March 11, 1895.  He there stated that the Arabs, “despite their slave-raiding propensities,” had “converted the Manyema and Malela country into one of the most prosperous in Central Africa.”  He also confessed that during the fighting the two flourishing towns, Nyangwe and Kasongo, had been wholly swept away.  In view of these statements the results of the campaign cannot be regarded with unmixed satisfaction.