In the chaos of the late 12th century, a chieftain named Temüjin finally succeeded in uniting the Mongol tribes between Manchuria and the Altai Mountains. In 1206, he took the title Genghis Khan, and waged a series of military campaigns – renowned for their brutality and ferocity – sweeping through much of Asia, and forming the Mongol Empire, the largest contiguous land empire in world history. Under his successors it stretched from present-day Poland in the west to Korea in the east, and from parts of Siberia in the north to the Gulf of Oman and Vietnam in the south, covering some , (22% of Earth's total land area) and had a population of over 100 million people (about a quarter of Earth's total population at the time). The emergence of Pax Mongolica also significantly eased trade and commerce across Asia during its height.