My Prediction:
In a remote area of New Mexico at the Black Mesa Research Facility,
a complex that bears many similarities to both the Los Alamos
National Laboratory and Area 51, an experiment that goes horribly
awry when an unexpected resonance cascade rips dimensional seams
that allow aliens from another world - known as Xen - to invade
Earth.
There are two sides: the hostile aliens, and the Hazardous
Environment Combat Unit, a military force dispatched to cover up
the incident—including eliminating the rest of the
scientists.
After 10 years, Earth's cities are renamed to City 1, City 2 -- and
so on, by the Combine.
City 17 is under the rule of a totalitarian administrator named
Doctor Breen, the former administrator of the Black Mesa Research
Facility. However, Breen is merely a puppet ruler who is carrying
out the will of the aliens known as the Combine. It seems that the
Combine mounted a brutal assault on humanity in which the forces of
Earth were completely overwhelmed in just seven hours
(appropriately referred to as the 7-hours War). The Combine now has
near-absolute control of the entire planet, with only a few pockets
of human resistance remaining. Doctor Breen enforces his rule (and,
by extension, the Combine's rule) through armies of intimidating
"Civil Protection" units (also called "Metropolice" or "Metrocops")
and Combine soldiers (referred to as the Overwatch).
