Its capital is the 1920s - inspired metropolis , Republic City .
The United Republic of Nations is a sovereign state founded by Avatar Aang and Fire Lord Zuko after the events of the original series as a haven for immigrants from all four nations .
United Republic of Nations ' capital is the 1920s - inspired metropolis , Republic City .
The United Republic of Nations is a sovereign state founded by Avatar Aang and Fire Lord Zuko after the events of the original series as a haven for immigrants from all four nations .