From 礼记·祭义: 'It is accurate whether extended to the Eastern Sea, Western Sea, Southern Sea or Northern Sea.' 四海 ('four seas') was the classical term for the whole world, with 中国 ringed by seas on all sides.
grammar
Classical structure: 放 (apply) 之 (it) 四海 (everywhere) 而 (and) 皆 (all) 准 (valid). Often used to claim broad applicability of a theory or principle.
