Treaty of Thronehold

The Treaty of Thronehold officially ended the Last War. 
The treaty recognized the following nations as sovereign states: Aundair, Breland, Darguun, the Eldeen Reaches, Karrnath, the Lhazaar Principalities, the Mror Holds, Q’barra, the Talenta Plains, Thrane, Valenar, and Zilargo. These nations abide by a common set of laws and maintain diplomatic relations. 
Note: the Demon Wastes and Shadow Marches have no unified government. Droaam, although it's declared itself as a nation, is not recognized by the treaty nations.
Sources:  Jeremy Crawford, James Wyatt, Keith Baker, Lead Designers. Eberron: Rising from the Last War. Wizards of the Coast, 2019.