It has been 20 years, since the Black Mesa Incident. 20 years since the incident that tore a hole between our dimension and the Borderworld, Xen. Through that hole never before seen forms of life emerged. It was clear from the first moment that their intentions were not peaceful. Though, through the heroic efforts of one Dr. Gordon Freeman, and many other security, science, and military personnel, the being keeping the hole open between our world and theirs was killed.

But it came with a great price. Xenian wildlife spread across the world, threatening people living in the country, away from sufficient military assistance. Billions in the world became refugees, flooding the metropolitan areas across the world. Entire countries collapsed because of the new crisis. Every other government was overwhelmed.

That's when they came. The only thing we could know about them was how they knew of us. Somehow they were able to detect the Black Mesa Incident, the accident's ripples across the pond of dimensions did not go unnoticed. It was only a matter of time until they found a way leading to our world.

They came in endless numbers, with weapons we thought were impossible; only the product of creative writers and authors. They were, from that point on very real to us. Even if we were prepared for them, we would've been annihilated to the very last man. Dr. Wallace Breen saw that, and knew that our only way of survival was collaboration with the so, he negotiated with them, and in the name of Humanity, surrendered unconditionally. All this happened in the span of seven hours. That's how the conflict was named "The Seven-Hour War". In recognition, Breen was appointed as the Administrator of Earth.

Following the war, the invaders, who were now known as the Universal Union or Combine settled into our planets, implanting their Citadels into the middle of remaining urban centers. Following this, the Transhuman Overwatch was set up, tasked with pacifying the planet, and being the fist line of defense in case of a hostile invasion. Slowly the initial invasion force withdrew from our planet, gradually placing the responsibility of keeping their newly conquered planet onto the shoulders of the newly-formed Overwatch, which numbers grew by the month.

That was 20 years ago. Most of Mankind came to accept their alien overlords. Many citizens joining into the ranks of Civil Protection, a quasi-police organisation tasked with keeping order, and ensuring the subservience of the population.

Now, in the central plaza of the largest urban center, named City 17, in which is the center of Combine rule over Earth located, a new portal began to open. The time has come for the Universal Union to expand once more.

Author's notes: Hey fellas, this is my first ever fanfic, so any kind of constructive criticism is appreciated. Suggestions are also welcome. I'll try and update this story as often as I can, but I'll make no promises.