(Covers information from Anderson's universe)
At the beginning of the Global T-Virus pandemic, the virus was reported in the city specifically, isolated from the rest of Maryland, with the rest of the epidemic concentrating on the west coast. Soon after, the city's population was all but destroyed, with fewer than 100 humans remaining after five years. A small gang of uninfected humans acquired a supply of food and guarded it with deadly force in the convention center. A former police officer named Jasper remained sealed in his own building, and the surviving citizens faced an unending struggle to survive.
Five years into the pandemic, Jill Valentine, the only survivor of the Raccoon City S.T.A.R.S. team, arrived in the ruined city and quickly made herself an enemy of the convention center gang. Appealing to Jasper as a fellow police officer, she gathered the remaining humans and led an assault to capture the convention center. After succeeding and established Baltimore as a haven for humanity, she planned to leave, but a Jasper's urging, stayed and became the leader of the enclave there.