This article contains spoilers. Read at your own risk!
It might spoil your gaming experience when first playing the related games.
The Seven Hour War was a brief, but decisive confrontation between the Combine and the governments of Earth, ultimately leading to a large human death toll and the Combine occupation of the entire planet.
The war itself is never discussed directly in Half-Life 2, but it is mentioned briefly by Eli Vance in Black Mesa East — looking at a small corkboard featuring several annotated newspaper cutouts and images causes him to reminisce about the events during the war. In Episode Two, Eli states that if the super-portal matures "it'll be the Seven Hour War all over again... except this time we won't last seven minutes!"
As the Portal Storms between Xen and the Earth raged across the planet, spreading Xen life forms across Earth, this caused the planet's populace to move into cities for protection. The Combine launched a surprise offensive, defeating all armed forces of all the nations on Earth in only seven hours, taking advantage of the confusion and chaos caused by the Portal Storms.
The Combine used the Portal Storms, which made a connection between the now conquered Xen - a crossroads of different dimensions - and Earth possible, to invade this universe. It was after this war that Dr. Wallace Breen negotiated a surrender on behalf of the United Nations, "saving" the survivors at the cost of their freedom. Breen was appointed ruler of Earth but remains under the control of the Combine. The official surrender appears to have taken place in New York City, in the United Nations building.
After the 7 hour war, the remaining humans were gathered in cities, with the world outside of such areas filled with wildlife native to other worlds. This made the the exteriors of cities and the regions beyond dangerous if not downright deadly to not only human life but also to the rest of Earth's natural fauna. The rest of the planet was reduced to inhospitable wastelands. Facilities like Nova Prospekt were opened within the remnants of the remaining man-made infrastructure- their goals being to modify humans, erase their memories, and assimilate them into the Combine's workforce and military.
The Combine also began to exploit the resources of Earth like water, which can be clearly seen in chapter Highway 17 and Sandtraps, where piers sit barren on the once watery shorelines where Earth's oceans had once occupied. The Citadel served as the only node to the Combine Overworld and Earth, as the portal storms were no longer furious on the planet and they could no longer use Xen as a connection. The Combine, since gaining dominance on Earth, has imposed a "Suppression Field," which serves to inhibit human reproduction and comments at the train station during Gordon's arrival suggest that the Combine has been drugging the populace through their water supply.
At the beginning of Half-Life 2, the G-Man makes a brief reference to the war, telling Gordon Freeman that "all the effort in the world would have gone to waste..." This is generally understood to be a direct reference to the war, the establishment of Dr. Breen's terror state, and the reasons for Freeman's stasis. Despite Freeman's triumph at Black Mesa, it was theorized that there was nothing that he or the entire human race could have done to save Earth from the superior forces of the Combine empire immediately after the events of Half-Life.
Half-Life 2 begins an undisclosed number of years after this war, and the rule of the Combine has been firmly established. There is, however, some evidence from the Half-Life 2: Episode One official website indicating that Half-Life 2 takes place nearly two decades after the Black Mesa incident. Such a time frame is logically consistent with the aging of the series' characters between Half-Life and Half-Life 2. This explains how Eli Vance's child, Alyx Vance, has matured to an adult since the events of the first game, where she was still an infant at the time. As for why there are no children in the game overall, the Combine had set up a reproductive suppression field for all of the remaining humans a short time after the war, preventing any further reproduction for approximately 20 years until the events of Episode One. However, the suppression field is disabled due to the damage the Citadel had taken thanks to Freeman's actions in Half-Life 2.
- ↑ Summary of Half-Life and Half-Life 2 in the official Half-Life 2: Episode One website. Retrieved on August 26, 2006.