Vault 15

Vault 15 was one of the Vaults built by Vault-Tec. It was supposed to stay closed for 50 years as part of the Enclave's Vaults experiments. It was also overcrowded. It contained occupants of diverse ideologies and ways of life, a situation that led to the schism, during which 4 groups of people left the Vault, three of which later became the Jackals, Vipers and Khans raiders, and the other one created the Shady Sands village.

Quotes
Vault 15 - "Unfortunately, we were crowded and life was very bad. There was a schism, and many people left, taking with them the best equipment.  Still, some of us tried to stay in the Vault.  But then we were attacked.  I was hurt, and I ended up here.  Now I try to help people..." - Katrina of Shady Sands