The history of the New Republic dates back to the survivors of Vault 15 who emerged from the shelter around 2097 and founded the town of Shady Sands. With the assistance of a Vault Dweller, who destroyed the local raider tribe, Aradesh and his daughter, Tandi, led the community into prosperity. With expanding trade routes came cultural exchange, eventually culminating in a movement aiming at forming a national entity. The idea resonated with other wastelanders and won popular support, leading to the formation of the New Republic in Shady Sands in 2186, with a trial council government established to draft the constitution. Three years later, in 2189, the Republic proper was voted into existence as a federation of settlements organized around a central major settlement.

Less than a century after its founding, the Republic is a model example of post-apocalyptic success and good ethics. Steady expansion and development led to widespread political enfranchisement, the establishment of rule of law and its enforcement, security from threats within and without (to a reasonable degree) and good standards of living across the southern wastes.