[Although overlooked, the CodeRED free FPS series, with the latest being Alien Arena, does have a story that mixes technologies available in the future with off-the-wall retro sci-fi from the Worlds of Tomorrow to help you understand the situation at hand, starting in the late-1940's with the crashland of the Roswell UFO...]
URF Chronological Timeline
1947 - Roswell
The Roswell UFO Incident occurs at Roswell, New Mexico, USA, as a spacecraft of obviously Alien origin - an Unidentified Flying Object (UFO) - crashes on this soon-to-be famous desert, possessing advanced alien technology termed "Xenotech". The UFO and its Alien crew - 2 dead, 1 live - were taken into a secret USM military base, nicknamed "Area 51", followed by a governmental coverup to ensure Xenotech reverse-engineering in the base was done behind tightly closed doors, up until 5 decades.
As an interesting note, during a UFO sighting - and a raid underway - at a Roswell farm in that year, URF Commander Joseph Hicks, during his mission in the 1st Martian War in 2049, happened to go back in time through a gateway and inflict heavy damage on the invading Martians, namely mortalizing several Martian Enforcers and dismantling a War Machine before he left for the gateway back into his time. Shocked to witness that the Humans are NOT as primitive as they are led to believe after all, the Martians saw this as a mortal setback in their invasion... but a setback nonetheless.
1950's-1990's - We are NOT alone
By the time of the Space Race between the USA and the SSSR that was in full swing, possibilities of extraterrestrial life from the final frontier rose, portrayed by science fiction movies - the most famous of which is Pál George's version of H.G. Wells' "War of the Worlds", and the most popular with kids being the controversially gruesome "Mars Attacks" trading card series found in bubblegum, with many a bizarre Maritan way of combat, ripe with blood 'n gore, all while men and women in Area 51 are working to the bone to unlock the secrets of advanced alien technology - zero gravity, energy weapons and robotics to name a few.
1999 - Xenotech Era
50 years of being cloaked in secret has led to this: the US Government has unveiled the advanced Xenotech long hidden in Area 51, all derived from technology found on the crash at Roswell, New Mexico, in 1947. That year changed the course of human history. The beginning of the 3rd Millenium was met with technological prosperity. In another fifty years, man lived in a world that is completely automated and populated by robotic assistance. But all good things must come to an end - one way or another. Without warning, the technology that man created turned against him...
The Mech Wars erupt, leading to the formation of the United Resistance Front (URF) that helped mankind survive these brutal wars that threatened to exterminate him. By the end of the Mech Wars several years later, civilization as we knew it was rebuilt by the survivors of these wars - among them being a decorated war hero, Lt. Commander (LCOM) Joseph Hicks, groomed for battle since birth. What man failed to realize that the Mech Wars were merely a prelude of something worse - namely a Martian invasion...
2049 - The Battle for Earth
LCOM Hicks continued to serve the URF, stationed at the Riker Containment Facility. All seemed to be routine and uneventful - until a number of aliens have been captured, raising many a question amongst the scientific community here. On top of that, Hicks' commanding officer, General Braddock, betrayed the URF and worked with alien invaders in their drive to add planet Earth as their first conquest, sparking the beginning of the 1st Martian War - however, during said war, Braddock wound up being betrayed - and disintegrated - by the Martians, conspiring Hicks to snap into immediate action.
Despite impossible odds, such as a collection of traps, enviroments and enemies, ranging from Martian warriors and mechs to hostile URF troopers to aggressive mechs, Joe Hicks, with an arsenal of weapons, of URF and Martian origin, and the help of his fellow URF Infantry soldiers, managed to blast his way right into the heart of the Martian military operation and assassinated the Martian "Big Brain", the one responsible for all this, thus ending the Battle for Earth. Hicks and the URF made the Martians pay DEARLY for the damage they have done on Earth - in green blood.
2055 - The Martian Chronicles
6 years have passed since the end of the Battle for Earth with the death of the last Martian Big Brain. Now a decorated war hero, Commander Joseph Hicks thought the Martian nightmare was over... but the worst is yet to come, as a new insurrection begun on Mars. He was the 15th man to be sent to quell it - all others before him have failed disastrously.
As expected, the Martians were quick to build a backup Big Brain, have assumed power, and have designs on building an army to annihilate all mankind as payback for their last war and achieve what the URF had them denied from: the conquest of Earth. Commander Hicks had no choice but to take the fight against the Martians to their homeworld, Mars, find the Big Brain, and take it down... and take it down he did, despite having a whole new army of Martian aggressors to deal with. Man has escaped death from the Martians yet again...
Present Day - Alien Arena
For time immemorial, involving the Earth-Mars Wars, up until now, has it been this way:
Planet at war with planet, conflicts ending with a burned cinder orbiting a dead sun and countless billions sent screaming into oblivion. War, endless and eternal, embracing all the peoples of the cosmos. Scientific triumphs heralded the creation of ever more deadly weapons until the very fabric of the universe itself was threatened. And the wars just kept escalating to the breaking point.
Until came the call, some said sent by an elder race, legendary beings of terrifying power who had existed since the birth of the stars and who now made their home beyond the fringes of known creation, others whispered fearfully and looked to the skies for the coming of their gods. Perhaps it didn't matter who had sent the call, for all the people of the stars could at least agree that the call was there.
The wars were to end - or THEY would be ended. In a demonstration of power and to get everyone's attention whoever had sent the call snuffed out the homeworld of the XXXX, the greatest empire of all the stars, in a heartbeat. One moment it was there, the next it was dust carried on the solar winds. All races had no choice but to heed the call. Even Earth and Mars were forced to lay their arms down and leave each other be. It was a distant tug, a whispered warning that the wars are all but over...
But for some warriors, for the greatest hero of each people, the call was more, it was a fire raging through their blood, a call to a new war, to the battle to end all battles. That fire burns in one such warrior's blood, compelling em, the greatest warrior of eir people, to fight in a distant and unknown arena, eir honor and the future of eir race at stake.
The call to battle beats through their hearts and souls like the drums of war. Only time will tell who shall be the one to rise through the ranks and conquer all others, the one who stands proud as the undefeated champion of the Alien Arena...