Wikipedia
Tianxia (tiānxià/tien-hsia; ) is a Chinese word and an ancient Chinese cultural concept that denoted either the entire geographical world or the metaphysical realm of mortals, and later became associated with political sovereignty. In ancient China, tianxia denoted the lands, space, and area divinely appointed to the Emperor by universal and well-defined principles of order. The center of this land was directly apportioned to the Imperial court, forming the center of a world view that centered on the Imperial court and went concentrically outward to major and minor officials and then the common citizens, tributary states, and finally ending with the fringe " barbarians".
The center of this world view was not exclusionary in nature, and outer groups, such as ethnic minorities and foreign people, who accepted the mandate of the Chinese Emperor were themselves received and included into the Chinese tianxia. In classical Chinese political thought, the "Son of Heaven" ( Emperor of China) , having received the Mandate of Heaven , would nominally be the ruler of the entire world. Although in practice there would be areas of the known world which were not under the control of the Emperor, in Chinese political theory the rulers of those areas derived their power from the Emperor.
The larger concept of tianxia is closely associated with civilization and order in classical Chinese philosophy, and has formed the basis for the world view of the Chinese people and nations influenced by them since at least the first millennium BC. Tianxia has been independently applied by other countries in the East Asian cultural sphere, including Japan, Korea, and Vietnam.