Geopolitical reference data from FAO
A key issue with building a semantic web is having robust base reference data, including geopolitical data such as the countries of the world. The Food and Agriculture Organization of the United Nations (FAO) has produced an ontology for geopolitical information that:
... manages information about territories and groups, such as, the different names in English, French, Spanish, Chinese and Arabic; associated classification codes, like, UN code -- M49, ISO-3166 Alpha-2 and Alpha-3, UNDP code, GAUL code, FAOSTAT, etc; historical changes; and specific relations like "x has border with y" and "x is member of group z".
That sounds like a great start, although I have not examined the details.