The First Alien War was a desperate conflict between the human race and the Cydonian Invaders, and the setting for the events of X-Com: UFO Defense. This war involved many clashes with the alien war machine, including shooting down and/or recovering UFOs, alien terror attacks on suburban towns, raiding Alien Bases, retaliation attacks on X-Com Bases, and ultimately a direct attack on the alien stronghold at Cydonia.
In the year 1999, sightings of Unidentified Flying Objects(UFOs) were reported across the globe. Rumors of cattle mutilation and insidious abductions began to spread like wildfire. The ruling parties of The United Nations were convinced that mankind was not alone. Orders were issued to mobilize all military forces to counter the alien invaders. Their efforts were proved fruitless, for they were too badly organized and unprepared for the alien incursion. The United Nations came to the decision to form an elite military division, with the best weapons and technologies available at their disposal and the greatest soldiers from around the world at their service. This secret organization was called the Extraterrestrial Combat Unit, or X-Com.
With X-Com founded, the war had officially begun. The first UFOs fell prey to the advanced "Interceptor" fighter jets, and elite soldiers and their equipment were carried to the battlefield with Russian "Skyranger" troop transports. When the war began, X-Com often skirmished with the calculating Sectoids and the stealthy Floaters, backed with robotic Cyberdiscs and voracious Reapers respectively. They fought upon the wrecks of UFOs and within suburban terror sites, in order to obtain alien devices and save the lives of innocent civilians from alien raiders.
Later in the war, the aliens recognized X-Com as a threat to their plans. At this realization, the aliens showed no mercy to the human resistance. They set up hidden bases on Earth, launched more brutal terror attacks and infiltrated the governments of nations that supported X-Com in order to reduce or withdraw funds to X-Com. New alien units were brought to the field, like the warrior Snakemen along with their terrifying Chryssalids and the ruthless Muton footsoldiers. It was not long until the Ethereals, the enigmatic alien masterminds, joined the fray too, taking part in missions and attacks against civilian targets and even X-Com's bases. At this point, X-Com had pinpointed the main alien base, located in the Cydonia region of Mars. The base was a massive underground stronghold that housed the alien manufacturing facilities and command centers. At its heart was a massive brainlike alien creature that directed the alien army. After arming themselves with the most powerful alien weapons and alien/X-Com hybrid technologies, a strike team flew to Mars aboard an X-Com "Avenger" spacecraft, to stop the alien hordes once and for all.
The Battle of Cydonia was long, difficult and costly. The X-Com strike team fought their way across the hilly surface of Cydonia, hounded by a horde of elite Sectoids with a full Cyberdisc escort. After finding the base's entrance within one of the five Cydonia pyramids, the team proceeded to storm the base interior. The base itself was even more difficult than the surface, with Mutons, Chryssalids and other terror units prowling the halls and Ethereals hammering the X-Com troops with Psi Attacks. After a long and perilous struggle, the Alien Brain was destroyed, causing the alien troops to die and the entire alien armada to grind to a halt.
The X-Com's victory at Cydonia marked the climactic end of the war. X-Com was disbanded shortly after the war's end, and the limited supply of alien technology was seized by the U.N.
Humanity was saved. The world was safe from alien incursion.
At least for now...