How Fallout's Vault 15 Ties Into the NCR

gamerant.com:

ByFallout: New Vegas, the New California Republic (NCR) is known as one of the largest factions in the Wasteland. They hold territories in Oregon, Nevada, and California, often providing protection to its citizens and governing trade. Their laws, ideals, and structure are based on old-world values such as democracy.

Before the NCR became as big as it is in Fallout: New Vegas, though, it had very humble beginnings. The faction would not have existed were it not for the existence of Vault 15 and the circumstances that happened there. It all began there, with a man named Aradesh.

Fallout: Every President of the NCR and What They Did

Vault 15 is a location that players could visit in the original Fallout and its sequel. Like all other Vaults, it was created with a social experiment in mind, and the experiment of Vault 15 was to gather radically diverse people in terms of culture and ideologies. The idea was to record their interactions.

Predictably, the vault dwellers were quite divided, which made most of the vault dwellers leave. They split and created different communities. One settlement, Shady Sands, was created with the vault's GECK. Many others did not quite make settlements, but became raiders with the Vipers, Khans, and Jackals. Some remained in the Vault itself, but that did not last long since the vault would eventually be attacked by raiders. The third level of the Vault caved in during a raider invasion, and those that remained inside either had to leave or perished. As Vault 15 fell to raiders, Shady Sands began to quickly develop. As it began to form, the leader of Shady Sands, who came out of Vault 15, would begin the creation of the NCR.

Shady Sands's leader Aradesh founded the settlement with the GECK in 2142.