All men within the four seas under heaven are brothers.
This is a quotation from The Analects of Confucius. The four seas refer to the seas on the four sides. The ancient Chinese thought that heaven was round and land was square, and China was located in the middle of the land, which was surrounded by four seas. The places within the four seas were all the territory known to them then.
The belief that "All men within the four seas under heaven are brothers" reveals the Chinese nation's concern for the whole world and kind offer of help to other people.
In his keynote speech at the Boao Forum for Asia Annual Conference 2015, Xi Jinping said: What China needs most is a harmonious and stable domestic environment and a peaceful and tranquil international environment. Turbulence or war runs against the fundamental interests of the Chinese people. The Chinese nation loves peace and has, since ancient times, held high such philosophies that "All men within the four seas under heaven are brothers."
四海之内皆兄弟
“四海之内皆兄弟”出自《论语》，意为全天下的人都亲如兄弟。“四海”即东海、西海、南海、北海，古人认为天圆地方，中国居陆地中间，陆地四周由四海环绕。“四海之内”指当时已知的人类生活空间，“四海之内皆兄弟”彰显了中国人兼济天下的博大胸怀、仁爱友善的人文精神。
2015年3月，习近平在博鳌亚洲论坛年会上指出，中国最需要和谐稳定的国内环境与和平安宁的国际环境，任何动荡和战争都不符合中国人民根本利益，中华民族历来爱好和平，自古就崇尚“四海之内皆兄弟”等思想。