The subsequent Han Dynasty ruled China between 206 BCE and 220 CE, and created a lasting Han cultural identity among its populace that has endured to the present day. The Han Dynasty expanded the empire's territory considerably with military campaigns reaching Korea, Vietnam, Mongolia and Central Asia, and also helped establish the Silk Road in Central Asia. Han China gradually became the largest economy of the ancient world. The Han Dynasty adopted Confucianism, a philosophy developed in the Spring and Autumn period, as its official state ideology. Despite the Han's official abandonment of Legalism, the official ideology of the Qin, Legalist institutions and policies remained and formed the basis of the Han government.After the collapse of Han, a period of disunion known as the period of the Three Kingdoms followed. In 580 CE, China was reunited under theSui. However, the Sui Dynasty declined following its defeat in the Goguryeo–Sui War (598–614).Under the succeeding Tang and Song dynasties, Chinese technology and culture entered a golden age. The Tang Empire was at its height of power until the middle of the 8th century, when the An Shi Rebellion destroyed the prosperity of the empire. The Song Dynasty was the first government in world history to issue paper money and the first Chinese polity to establish a permanent standing navy. Between the 10th and 11th centuries, the population of China doubled in size to around 100 million people, mostly due to the expansion of rice cultivation in central and southern China, and the production of abundant food surpluses. The Song Dynasty also saw a flourishing of philosophy and the arts, as landscape art and portrait painting were brought to new levels of maturity and complexity, and social elites gathered to view art, share their own and trade precious artworks. Philosophers such as Cheng Yi and Chu Hsi reinvigorated Confucianism with new commentary, infused Buddhist ideals, and emphasized a new organization of classic texts that brought about the core doctrine of Neo-Confucianism.