Colonization of the Congo Basin refers to the European colonization of the Congo Basin of tropical Africa. It was the last part of the continent to be colonized. By the end of the 19th century, the Basin had been carved up by European colonial powers, into the Congo Free State, the French Congo and the Portuguese Congo (modern Cabinda Province of Angola). Early European exploration One by one the other great mysteries had been explored: The coasts by Prince Henry the Navigator's Portuguese sailors in the 15th century. The Blue Nile by James Bruce in 1773. The remote upper Niger by Mungo Park in 1796. The vast Sahara by competitors Laing, Caillié, and Clapperton in the 1820s. The fever-ridden mangroves of the lower Niger by the brothers Richard and John Lander in 1830. Southern Africa and the Zambezi by Livingstone and John Clafton in the 1850s. The upper Nile by Burton, Speke, and Baker in a succession of expeditions between 1857 and 1868. Though the Congo had been one of the first to be attempted, it remained a mystery. Since the 15th century, European explorers had sailed into the broad Congo estuary, planning to fight their way up the falls and rapids that begin only inland, and then travel up the river to its unknown source. All failed. The rapids and falls, had they known it, extended for inland, and the terrain close by the river was impassable, and remains so to this day. Repeated attempts to travel overland were repulsed with heavy casualties, accidents, conflicts with natives, and, above all, disease saw large and well-equipped expeditions got no further than or so past the westernmost rapid, the legendary Cauldron of Hell. Stanley's exploration It was not until 1867 that the Congo was explored by Europeans, and even then it was not from the sea, but from the other side of the African continent. Setting out from Zanzibar, Henry Morton Stanley, a British-born American journalist and explorer aimed to find the famous Dr. Livingstone. Livingstone had not been heard from in several years and was, in fact, exploring the upper reaches of a great navigable inland river called the Lualaba, which Livingstone hoped was connected to the Nile, but which turned out to be the upper Congo. After leaving Livingstone, Stanley sailed for 1,000 miles (1,600 km) down the Lualaba (Upper Congo) to the large lake he named Stanley Pool