Global T-Virus pandemic

Following the outbreaks of the T-Virus in The Hive and Raccoon City, the entire planet was consumed in a pandemic, killing most of humanity.

The Hive
The spread of the virus has it's genesis in the incident in The Hive a top secret research facility of the Umbrella Corporation dedicated to the development of the T-Virus as a biological weapon. However, the facility had been infiltrated by an anti-Umbrella agent named Lisa Addison, whose purpose was to obtain a sample of the virus as evidence. Her activities were discovered by the Hive's security chief, Alice, and the two began conspiring together.

Unbeknownst to either of them, Alice's partner, Spence Parks, was also planning to steal the T-Virus for sale on the black market. Having done so, he delibrately unleashed it within the Hive to cover his tracks. The facility was sealed by the AI known as the Red Queen, and it's five hundred employees were systematically killed. A commando team was sent in to investigate, and after a protracted struggle, the only survivors were Alice and Lisa's brother, Matt Addison. They were taken prisoner by Umbrella, and experimented on in nearby Raccoon City.

The Fall of Raccoon
It could have ended there, had Major Timothy Cain not foolishly decided to re-open the Hive and investigate. Within thirteen hours, zombies and lickers had spread the virus all across Raccoon City. A wall was constructed and security measures were swiftly put into place around the city. What few survivors remained were trapped in a necropolis dominated by the Undead.

Eventually, the decision was reached by Umbrella to sterilize the city. A thermonuclear device was launched at sunrise, but not before five survivors, Alice, Jill Valentine, Carlos Oliveira, Lloyd Jefferson Wayne, and the young Angela Ashford, escaped via helicopter with evidence of Umbrella's crimes.

The Nightmare Continues
Despite the survivors' best efforts, Umbrella managed to cover up the incident. But they had made a fatal oversight. A single scientist, Dr. Jim Knable, had been unknowingly infected, and transported to San Francisco. He soon succumbed to it's affects and began infecting others. Attempts were made to confine the outbreak to the Mission District, but it was already too late. Unsuspecting carriers had already boarded airplanes, and by the time the President of the United States was briefed on the nature of T-Virus, there were already carriers inside the White House itself.

At the suggestion of his Science Division Head, Dr. Sam Isaacs, Umbrella Chairman Albert Wesker began moving corporation assets to the various underground facilities maintained throughout the world. The corporation would soon become the only intact entity with the ability to effectively defend itself.

Worldwide Destruction
It wasn't long before the rest of Planet Earth suffer the same fate as the United States. Every attempt at confining or suppressing the infection failed, and humankind entered a new dark age as the world was overrun by the undead.

Survivors, what few there were left, stayed on the move. Speed and mobility were the best defense against the the zombie masses. The convoy lead by Claire Redfield was one such example.

Occasionally, the humans would be aided by nature. Swarms of infected crows were known to feed on flesh, infected or otherwise. The entire undead population of Las Vegas was purged in this manner.

On the other end of the spectrum, there were survivors who remained in their cities, defending themselves vigorously. It is known that a community in Alaska remained safe by virtue of it's isolation. Baltimore was another such place, home to more than a hundred humans who managed to eke out a living among the ruins.

Hope
Through his experiments, Sam Isaacs came to realize that Alice, who by now was a superhuman wandering the country, was the key to humanity's survival. Her blood, which had adapted and changed the T-Virus, could lead to a total cure, granting total immunity to the pathogen's ravaging effects.

Alice herself was eager to help, having been running from the corporation for five years. Although it is still unknown if she succeeded in creating a cure with the help of the White Queen, she vowed to make Umbrella pay for their actions.

Survivors
The spread of the T-Virus was devastating, but not absolute. According to the White Queen's sattelite scans, out of the planet's pre-outbreak population of 6.5 billion human inhabitants, there were 1,733,548 people still alive on the surface.