Amu Darya's course across the Karakum Desert has gone through several major shifts in the past few thousand years. Much of the time – most recently from the 13th century to the late 16th century – the Amu Darya emptied into both the Aral and the Caspian Seas, reaching the latter via a large distributary called the Uzboy River. The Uzboy splits off from the main channel just south of the river's delta. Sometimes the flow through the two branches was more or less equal, but often most of the Amu Darya's flow split to the west and flowed into the Caspian. People began to settle along the lower Amu Darya and the Uzboy in the 5th century, establishing a thriving chain of agricultural lands, towns, and cities. In about AD 985, the massive Gurganj Dam at the bifurcation of the forks started to divert water to the Aral. Genghis Khan's troops destroyed the dam in 1221, and the Amu Darya shifted to distributing its flow more or less equally between the main stem and the Uzboy. But in the 18th century, the river again turned north, flowing into the Aral Sea, a path it has taken since. Less and less water flowed down the Uzboy. When Russian explorer Bekovich-Cherkasski surveyed the region in 1720, the Amu Darya did not flow into the Caspian Sea anymore. By the 1800s, the ethnographic makeup of the region was described by Peter Kropotkin as the communities of "the vassal Khanates of Maimene, Khulm, Kunduz, and even the Badakshan and Wahkran." An Englishman, William Moorcroft, visited the Oxus around 1824 during the Great Game period. Another Englishman, a naval officer called John Wood, came with an expedition to find the source of the river in 1839. He found modern-day Lake Zorkul, called it Lake Victoria, and proclaimed he had found the source. Then, the French explorer and geographer Thibaut Viné collected a lot of information about this area during five expeditions between 1856 and 1862. The question of finding a route between the Oxus valley and India has been of concern historically. A direct route crosses extremely high mountain passes in the Hindu Kush and isolated areas like Kafiristan. Some in Britain feared that the Empire of Russia, which at the time wielded great influence over the Oxus area, would overcome these obstacles and find a suitable route through which to invade British India