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The government fell with the face of humanity after Outbreak Day. Some humans survived, but you could barely call the survivors human. Sections of the army spread out into different areas of America. They took control of the largest hospitals in the states. It had many resources, after all: beds, water, food, and medicine. However, any sick left in the hospitals after the outbreak were killed on the spot, and doctors were ordered to create a vaccine.

Slightly inspired by The Last of Us
Post-Apocalyptic world
They're all part of the Alphabet mafia