Excerpts from Books and Wikipedia
"For more than two centuries, the Zhou dynasty seemed to enjoy heaven's blessing. . . . The weakness of the king became clear in 771 B.C., when attacks by nomads forced the Zhou to abandon their capital in western China and establish a new capital at Luoyang, to the east. . . . As the kingdom slowly fragmented into rival states, some people longed for the return of strong rulers who would govern China wisely with a mandate from heaven." [National Geographic Almanac, p. 61]
"With the conquest of the Shang dynasty by the Zhou, the Chinese state finally emerges. . . . After they finally settled in the Wei River valley, the Zhou rulers became vassals of the Shang until they became strong enough to conquer Shang in warfare in about 1040 BC. . . . The victorious Zhou built a new capital at Xi'an (Chang'an). . . . While the Zhou thus continued, like the Shang, to use kinship as a main element of political organization, they created a new basis of legitimacy by espousing the theory of heaven's mandate. . . . This doctrine asserted the ruler's accountability to a supreme moral force that guides the human community." [Fairbank: China, p. 39-40]