Before the arrival of Europeans in the region, Buganda was an expanding, "embryonic empire".[12] It built fleets of war canoes from the 1840s to take control of Lake Victoria and the surrounding regions and subjugated several weaker peoples. These subject peoples were then exploited for cheap labor.[12] The first Europeans to enter the Kingdom of Buganda were British explorers John Hanning Speke and Captain Sir Richard Francis Burton while searching for the headwaters of the Nile in 1862. They found a highly organized political system which was marred, however, by the ongoing practice of mass human sacrifice estimated at 800 persons annually.