The Yuezhi were an ancient people first described in Chinese histories as nomadic pastoralists living in an arid grassland area in the western part of the modern Chinese province of Gansu, during the 1st millennium BC. After a major defeat at the hands of the Xiongnu in 176 BC, the Yuezhi split into two groups migrating in different directions: the Greater Yuezhi and Lesser Yuezhi. This started a complex domino effect that radiated in all directions and, in the process, set the course of history for much of Asia for centuries to come.