Humanity. We thought of ourselves as the master-race: the top of the food chain. The ultimate predator. We waged our petty wars over our planet, its finite resources all but gone as the armies of the world's nations squabbled over the miniscule amounts remaining.

These wars escalated into massive, continental struggles. We launched all manner of nuclear and chemical weaponry: wiping entire nations off the globe. America and China fought on: many tiny countries between the two behemoths becoming collateral damage in a war of which nobody could remember the cause.

But even as Humanity tore itself to pieces: other races regarded Earth: sizing it up and biding their time. They waited until we were at our weakest and then they struck.

The Combine came first: Portals, great rends in time and space, tearing open worldwide. Our atmosphere went crazy: massively destructive storms ravaged outlying settlements and strange, feral alien predators began to appear. People migrated, en masse, to the cities for safety. That was when the Combine's armed might appeared. For seven hours they came: an unending tide of monstrous walkers, tanks and aircraft that overwhelmed the military might of all the world's nations and occupied its cities. It took humanity thousands of years to establish itself in countries and governments: protected by armies and machines. It took the combine seven hours to undo it all.

Beset by this terrible threat, the armies of the government retreated. Seven hours of fighting and they were all but defeated: the remnants hiding in the few cities and towns remaining under human control.

The invasion of the Combine: their portal technology in particular, sent ripples through space and time and the escalated violence on the surface of Earth attracted a new aggressor. The so-called Locusts. These brutish creatures: like a horrifying cross between man and ape, emerged from the very ground itself: climbing from great fissures and sink holes which began to appear across the planet.

The Combine: alarmed at the new threat and caught unawares, suffered heavy casualties in the first weeks of fighting. By some massive coincidence: the largest emergence-hole-affected areas opened up on the narrow land-bridge between North and South America: turning back the Combine's "Extermination Forces" who were on their way up to finish the last of the United Nations forces hiding in the far north.

These newcomers were, by no means on the side of the humans, however. The Locusts in North America seemed more interested in the Combine bases to the south, but small units of Locust Drones began to scout to the north and soon the reprieve that the survivors of the seven-hour-war had received was ended as the monsters engaged our troops in skirmish battles.

The Locusts made no effort to either contact humans or combine, and thus their motive was unclear. Locust tactics seemed to be one of Genocide: destroying and slaughtering everything in each designated zone before regrouping and moving on.

As the UN troops fought on, they became a beacon of hope to refugees and civilians, who fled their Combine prisons and rallied to these few, brave troopers. What was once a small town they were using as a base was repopulated and swelled by the weight of people fleeing there. This town, its old name long-forgotten, was simply named 'Sanctuary', for that was what it was: a safe place: both because of its garrison and its geographical location: a deep valley with little or no road access.

And so, with the Combine and the Locusts locked in a grim stalemate war in the outside world, Humans began to build. They used scavenged weapons and technology to produce armor, guns, tanks, walls. In those early days, there was no shortage of volunteers, either: people fleeing the Combine's Police-State cities or the Locust's murderous Crusade gladly accepted the opportunity to fight back. But there were still not nearly enough soldiers to take the fight to the enemy.

So humanity sat and waited. We watched as the two alien forces clashed again and again: waiting for the first sign of weakness…