User blog comment:KrusH HsurK/Earth, Capital of humanity, but lacking of its own capital?/@comment-67.250.95.164-20120508213008

They made it clear in the past two games that Earth was a coalition of separate governments, but they all came under the Systems Alliance-whose capital is Arcturus Station. They did mention in the Stealing Memory DLC in the Kassa Locust gun info that it was used against the Presidents of the United North American States, the European Union, and the Chinese People's Federation-cities like Mexico City still exist, though they're probably not capitals since Mexico City for example, is in the UNAS.