If this sounds like your idea of a really good time, be prepared to work for it. Only a guild with an upgraded Aurorian castle can form a nation, and even then there’s a a pack to create and transport, a general to kill, materials to gather, and even more tasks to accomplish. Joining a player nation, however, is a tad easier: You just have to be unguilded. For full details on how to form a nation, check out the nation spotlight.
ArcheAge’s NPC factions? Or maybe you just want to wear spiffy new clothes and raise a wyvern mount? You will have that chance when Ascension launches. More than just building cities, this upcoming expansion will allow players to create whole nations, which are player factions. Nations will have their own player Sovereign (who gets the clothes and the mount), include up to 10 additional players as their Hero Council, and allow all races to work together and fight alongside each other without resorting to piracy. A player nation can also earn taxes, make treaties, and fight as a separate entity in PvP battles as well as expand their claim on Auroria by conquering castles.
Source: Official site; thanks Ernost for the tip