Within the Four Seas
Within the Four Seas means within the territory of China. The ancient Chinese thought China’s territory was surrounded by the Four Seas (the East, West, North, and South seas). Within the Four Seas refers to the landmass surrounded by the Four Seas. It reflected the ancient Chinese belief that the seas were the natural boundary of a country, demonstrating the influence of an agriculture civilization.
If our country wants to conquer all under heaven, rise above the big powers, subdue enemy states, control the territory within the Four Seas, govern the subjects and rule over the feudal lords, military force is indispensable. (Strategies of the Warring States)
If you have a bosom friend within the Four Seas, even at world’s end he remains close to you. (Wang Bo: Seeing Off a Friend Who Has Been Appointed to a County Post in Shuzhou)