Gate: Remnant of the Earth's Coalition.

During the Seven Hour War, a unit of 15 men, consisting of the National Guard unit, local SWAT, remnants of an infantry battalion, and remnants of HECU Marines, were overwhelmed by the Combine and Xen forces. The unit escaped from the battlefield, and the Earth's military, already spread thin due to the Black Mesa Incident, released the wildlife of Xen to the environment of Earth.

While they were in the mids of retreating, they managed to enter a gate disguise as an ordinary building and there on that day, lives of the 15 men suffered the same fate as Gordon and Adrian have met their own.

"How will the world of Gate [Inhales] react to this event? We shall see..." - Mysterious Man