The Han dynasty (206 BCE – 220 CE) was the second imperial dynasty of China, preceded by the Qin dynasty (221–207 BCE) and succeeded by the Three Kingdoms (220–280 CE). It was founded by the rebel leader Liu Bang, known posthumously as Emperor Gaozu of Han. It was briefly interrupted by the Xin dynasty (9–23 CE) of the former regent Wang Mang. This interregnum separates the Han into two periods: the Western Han (206 BCE – 9 CE) and Eastern Han (25–220 CE). Spanning over four centuries, the period of the Han dynasty is considered a golden age in Chinese history. To this day, China's majority ethnic group refers to itself as the "Han people" and Chinese characters are referred to as "Han characters". The Han Empire was divided into areas directly controlled by the central government, known as commanderies, and a number of semi-autonomous kingdoms. These kingdoms gradually lost all vestiges of their independence, particularly following the Rebellion of the Seven States. The Xiongnu, a nomadic confederation which dominated the eastern Eurasian Steppe, defeated the Han army in battle in 200 BCE. Following the defeat, a political marriage alliance was negotiated in which the Han became the de facto inferior partner. When, despite the treaty, the Xiongnu continued to raid Han borders, Emperor Wu of Han (r. 141–87 BCE) launched several military campaigns against them. The ultimate Han victory in these wars eventually forced the Xiongnu to accept vassal status as Han tributaries. These campaigns expanded Han sovereignty into the Tarim Basin of Central Asia and helped establish the vast trade network known as the Silk Road, which reached as far as the Mediterranean world. Han forces managed to divide the Xiongnu into two competing nations, the Southern and Northern Xiongnu, and forced the Northern Xiongnu across the Ili River.