August 1, 1998
The Kiryu-Kai is established by Japan.
December 1, 1988
After months of expensive operations, not a single UFO is intercepted by the Kiryu-Kai.
December 11, 1988
Representatives of the world's most powerful nations gather in Geneva to discuss the alien problem and find ways to counter it.
Kiryu-Kai's existence is revealed to the representatives to a surprising lack of condemnation.
A new international organization is created to counter the alien problem and is named the Extraterrestrial Combat Unit
January 1, 1999
X-COM begins operations in Europe to resounding success, having downed a UFO and retrieved it in the first week.
X-COM begins research into deuterium fluoride laser technology, having found that its equipment is insufficient to counter the alien threat.
A side research project is also started by X-COM to investigate the strange material that the UFO's are made of.
January 15, 1999
X-COM's laser research has paid off. They have managed to design and build a man-portable laser weapon, which was until now the purview of science fiction. This weapon quickly displaces regular projectile weapons in X-COM service, hitting harder, with an "ammunition" load so large that reloading is not a tactical consideration and a much higher accuracy.
In this short time two more UFOs are shot down and retrieved at a high personnel cost.
February 1, 1999
X-COM's side project is completed, the Alien Alloys are capable of being reproduced by X-COM. Research is immediately switched to discovering a method of producing armour to from this material to lower casualties.
A landed UFO is successfully retrieved and along with it an intact UFO engine and some strange material that seems to be powering it.
Research is started into the strange material that powers the UFOs.
February 5, 1999
Basic armour is now capable of being produced from the Alien Alloy. It is estimated to be able to reduce casualties by fifty percent.
Research into the crystal is slow going; it is discovered that the material is a new element with an atomic number of 115.
Another landed UFO is retrieved and an alien navigator is captured.
February 15, 1999
Casualties have dropped by the estimated fifty percent thanks to the new armour.
The crystal has been discovered to be a power source for most of the alien technology. It is named Elerium and discovered to be impossible to synthesize with current technology.
Research begins into replicating alien plasma weaponry and alien spacecraft technology.
A lucky intercept of a battleship allows X-COM to capture a Sectoid leader.
Interrogation of the alien navigator begins.
March 1, 1999
The power source is figured out but the navigational system of the alien craft is still being puzzled over.
X-COM's first encounter with psionics occurs. It is a curb stomp and the craft returns with only two soldiers left.
Interrogation of the alien leader begins.
Interrogation of the navigator is complete. Research into alien communications technology begins.
Old power armour designs are dug up and implemented with an elerium power source, circumventing the enormous power drain by their systems.
March 4, 1999
Interrogation of the alien leader is complete with some disturbing information gained. The Martian solution is tabled.
A new field is opened, psionics, construction of a psionic lab begins immediately. As one scientist jokes, "Only mind control can defeat mind control."
Aggressive research has paid off; the first elerium powered craft; the Firestorm, is designed and built, being marred by flaws that mar all first generation elerium powered crafts. Luckily, compared to the standard interceptor, it is exceedingly efficient at the task it is designed for, but compared to the original interceptor; it does not perform its unofficial tasks so well.
April 5, 1999
The psionic lab is completed and the first batches of soldiers enter it for evaluation and training.
As they train, research begins into the production of a device that will allow these soldiers to use their psionic potential.
A new transport is designed based on the Firestorm. It is an abyssal failure but its design and prototype construction teaches the research team new lessons about elerium powered ship construction.
Plasma based weaponry find its way onto X-COM crafts, and into the hands of its operatives, the low level research into alien plasma weaponry finally paying off and X-COM's great stocks of "obtained" plasma weapons finally being released.
A decoder for alien communications is produced. It provides a hundred percent detection rate of UFO's.
April 15, 1999
With twenty days to go, a device is invented; tested and produced that allows trained soldiers to use psionic potential.
May 5, 1999
Fortunately, most of X-COM's troops are psionicly capable. The new psionic capabilities further reduce X-COM casualties.
X-Com realizes it is fighting a losing battle and decides to perform a strike at the alien leadership on Mars, before they are overwhelmed. X-COM begins an aggressive campaign of capturing alien leaders to discover the location of the alien base on Mars.
The first alien retaliation missions hit X-COM bases. They are barely fought off, at great cost in personnel and equipment.
Another attempt at designing a new craft finally gives X-COM the Avenger, an otherwise perfect vehicle other than the flaw with first generation elerium engines. It is capable of, and otherwise does, barring the scarcity of elerium, replace the Skyranger troop transport.
December 31, 1999
New Year eve is celebrated by X-COM with the capture of an alien leader. Interrogation is begun immediately, searching for the alien base on Mars.
January 12, 2000
The retaliation mission is prepped and sent, results being awaited for with abated breath.
January 14, 2000
The retaliation mission was successful, and with the destruction of the alien brain, the remaining aliens are uncoordinated and easy to finish off. A distress beacon is set off at one of the last pockets of alien resistance.
Worried, X-Com steps up preparation, finding an alternate supply of elerium or human alternatives to elerium based tech. The first generation elerium crafts are decommissioned as elerium becomes scarce.
March 20, 2002
RDA is formed.
Colonization of the solar system is accelerated by the presence of alien tech and promise of bountiful resources. Two self sustaining colonies are built on the Moon with five more in the pipeline.
Small elerium deposits are found on the Moon and Mars.
May 15, 2005
The survivors of the first alien war, who have been discharged from active service, get together and start a weapon company named Marsec.
January 1, 2041
Ships start disappearing along international trade routes.
X-Com is now a salvage organization, focused on recovering the hundreds of underwater UFO wrecks for precious elerium. This X-COM finds disturbing evidence that there is a new alien threat and goes into action secretly with repurposed technology.
February 15, 2041
Thanks to a robust research process, this X-COM has developed a new class of weapons based on the theories behind plasma weapons, called, Gauss weapons. They have the advantage of not needing elerium.
Aqua plastic is discovered, and immediately researched. It is nearly as tough as Alien Alloys but more flexible.
February 15, 2041 – February 15, 2046
In these five years, X-Com fights off the aliens, recovering tech and reverse engineering it, allowing access to sonic weaponry and a new energy source called Zrbite. The alien's base deep under the sea is discovered and assaulted. The alien's leader's life support is destroyed and the remaining alien bases are destroyed piecemeal. Sadly after the destruction of the base, Zrbite become powerless lumps of gold.
Pandora is discovered.
January 14, 2104
Dr Grace Augustine is born.
June 22, 2129
Jake and Tom sully are born.
July 12, 2139
RDA is given rights to exploit Pandora's natural resources.
Dr Grace Augustine arrives on Pandora.
March 19, 2144
Global war erupts over diminishing reserves of elerium. Jake Sully is paralyzed in combat.
May 21, 2146
The war ends in a draw and the Scorched Terra agreement is signed. Further warfare on Earth is banned.
June 21, 2148
Tom Sully is mugged and killed
Jake Sully is approached by RDA operatives and offered the chance to join the avatar program. He accepts.
July 28, 2148
Jake Sully leaves for Pandora.
May 12, 2154
Jake Sully and Norm Spellman arrive on Pandora. They meet Grace.
Sectoid UFO's are detected on Pandora from orbit. This is reported to Earth. As soon as Earth receives the message, Hell's Gate is taken over by X-COM. The Avatar negotiation project is canceled.
Parker Selfridge is removed as head of operations at Hell's Gate and Quartich is also removed from his position as head of Security. A command structure is pieced together from old X-COM operatives on Pandora, of which there is a surprising amount of.
To X-COM players, the one year plus victory is real. It needed liberal amounts of luck and save-scumming but it is real.
I skipped a lot of TFTD because I was not so hot at it. I could not win and therefore lacked a timeline.
Any request for more background?