There was that awesome space shooter, "FreeSpace".
In Freespace 1, Mankind discovered wormholes, begins colonization of connected systems. It becomes the GTA (Galactic Terran Alliance). Then the GTA encounters a "civilized", space-faring alien species, the "Vasudans" (Vasudan Empire). Mutual defiance quickly escalate to an all-out war between the two species. Both fleets have comparable strenght, and the war rages for years, exhausting resources without decisive victories.
Then xenophobic alien invaders owning superior technology come out of nowhere. Ignoring any communication attempts, they tear through the rank of both fleets, without any preference. Terrans name those newcomers the "Shivans". Their EM shields make their fighters extremely though, and Terran or Vasudan hull plating is of little use. Against the upcoming disaster, former ennemies make peace and form a new alliance, the GTVA (Galactic Terran-Vasudan Alliance). The Terrans manage to disable a small Shivan frigate and to board it with space marines. Shivans encountered are extremely dangerous 5-legged insectoids, likely products of bio-engineering. Scientists are able to retrofit the EM shield technology on allied fighters, which seriously even the odd (though Shivan fighter still have better propulsion and weapons). Then the Shivan mothership enters the battle, and no weapons in the alliance can harm her mighty EM shield.
System after system, the dreadnaught closes from Vasuda Prime (Vasudan home system/planet) and fire massive particle beams weapons at the surface that release insane energy on impact (each hit is pretty much equivalent to a nuclear warhead). Terrans make what they can to help Vasudans to evacuate as many as possible. Still, after hours of heavy bombardment, the planet is an unhabitable desert. The situation becomes critical as the Shivan mothership is invulnerable, and has two huge beam cannons that slice Terran or Vasudan capital ships like bread. The death toll in the alliance ranks rises and military resources are getting scarce.
Worse, the Shivan dreadnought re-route towards Sol, which is virtually defenceless. It still has to get through wormhole "subspace" nodes, so the Terran and the few Vasudan capital ships stills available try a last-stand defence on the way. It goes horribly wrong and the Shivan destroyer heads towards the last node unharmed.
Meanwhile, Alliance xenologists have made a series of archeological discoveries scattered on the Terran-Vasudan space. It seems that another species, the "Ancients", was there 10,000 years ago. Their left records behind them. Like Terrans or Vasudans, the Ancients discovered wormholes, expanded, and encountered new species. They fought them all and crushed them. Then the Shivans came and destroyed their huge empire system after system. Ancients lose battle after battle. Their empire was so huge they first evacuated the threatened systems, hoping that it would be enough to calm down the invaders. But they were tracked to they home system and exterminated. On their last days, Ancient thinkers understood that the hive-minded Shivans were sensitive to wormhole activity, and attracted by it. And, most importantly, that their shields could not work inside a wormhole.
The GTVA then sends a few remaining frigates and a wing of attack fighters inside the wormhole leading to Sol, right behind the Shivan mothership. The transit lasts only 10 minutes, during which Terrans starfighters manage to launch their bigger bombs on the massive destroyer fusion reactors. The dreadnought is half-exit in the Solar System, but has suffered critical damage, and explodes, half-inside, half-outside the wormhole. That uncommon situation causes the wormhole to collapse completely, severing the Earth from the GTVA space.
Freespace 2 takes place 40 years later. Terrans have no news of the Earth, now severed of the Alliance space and too far away for near-lightspeed communications. The GTVA stayed united and rebuilt a strong fleet, using a mixture of Terran and Vasudan technologies to build advanced warships and fighters. The fleet also accounts old capital ships that fought during what is now called "The Great War". Every fighter is now equipped with shields, and the Shivan particle beams technology has been retro-engineered and adapted on most warships, giving the fleet a huge firepower boost. Terrans managed to design flak guns operating in space, ballistic weapons sending a lot of shrapnel, and equipped the fleet with as much as they could. Even more, both species began together the building of an enormous dreadnought, the "Colossus", twelve times bigger than the Shivan mothership encoutered 40 years ago. The enormous beam cannons of the beast can turn anything into ashes, while it is vast enough to maintain dozens of fighter/bomber wings. The Alliance seems ready.
But there are internal political conflicts : Terran extremists (pretty much Neo-Nazis) make a coup. They want to resume the war against Vasudans. A significant part of the Terran Fleet join the rebels which get strong enough to assemble a fleet and become a credible threat to the GTVA. They commit numerous atrocities and war crimes against Vasudan civilians. Their talented admiral use hit-and-run tactics that renders the enormous GTVA war machine inefficient. Things get pretty nasty as some Vasudan systems have to be evacuated. But the Colossus test phase is over and the monster ship is sent in. Its firepower obliterates the NTF capital ships and cause waving in the ranks. Finally, rebels surrender and the admiral escapes with a few fanatics into an uncharted wormhole through a strange, ring-like giant structure made of moving parts. First analysis show it was crafted by the Ancients 10,000 years ago, and seems to act as a wormhole "stabilizer".
The GTVA sends an exploration party through the wormhole, which appears to lead into a dense nebula. Static storms and overhelming EM radiation make long-range communications impossible, while the visibility is awful. Soon a fighter wing goes missing. The SAR party stumbles upon Shivan fighters, and a crippled NTF warship begging for rescue, saying that the rebel Admiral left them behind and headed for another node, escorted by Shivans. Allied Command agrees to rescue the rebels, but the warship is wiped out by a wing of Shivan bombers coming out of the mist.
It turns out that the Admiral found a way to communicate (in a very primitive fashion) with the Shivans. Lost for lost, he wanted to attract them into GTVA space. He was last seen boarding what looked like a Shivan transport. His fate is unknown.
The GTVA, rejoycing after the victory over the NTF and very confident in the Colossus firepower, decides to send several fleets into the Nebula in order to track down and exterminate as many Shivans as possible. The goal is to achieve a preemptive strike, in order to avoid by any means a replay of the Great War scenario. It turns out that Shivan technology also improved, but that their new warships are nothing like the shielded mothership encountered 40 years ago. With the advantage of the initiative and smart tactics, the allies seem to be in control in every battle.
Then a new Shivan fleet arrives in the Nebula, backed up by a new kind of mothership. The juggernaught is as big as the Coloussus, which much more massive. The GTVA still has a comfortable advance in numbers and tactics, so a strategic retreat is decided into the system (Capella) leading to the Nebula. A blockade is set-up, keeping the Colossus as a reserve. It appears that the Juggernaught has beam weapons of an unthinkable magnitude. Its sheers mass also makes it extremely though. A fleet is left into the Nebula, and perform a surgical strike on the monster's beam cannons before retreating.
The Juggernaught warps in Capella with a fraction of its firepower. It still proves to be a match for the Colossus. But the allied dreadnaught attracts much of the enemy fire, leaving room for starfighter strikes on the Shivans remaining beam cannons. The Colossus own beams then finish the job. While seriously damaged, the allies capital ship is still in one piece and can safely head to the shipyards for repairs.
However, GTVA intelligence isn't completely blinded by the victory and decides to probe beyond the Nebula via the newly discovered wormhole. To achieve this, they manage to disable and capture several Shivan fighters, and adapt Terran or Vasudan life support/controls to it. The infiltrators emerge in an unknown star system, guarded by previously unseen Shivan static sentry guns. They also detect an apparently endless trail of Shivan juggernaugths, pouring from another portal-like structure and heading to the Nebula. This is of course a disaster, as a single of those ships proved to be an extreme challenge. Worse, the Colossus is under repairs.
The GTVA hasn't many choices. They know the Shivans will obliterate their population centers if they have any chance to do so. While the Shivan vanguard flows into Capella, a counter-offensive is planned in order to destroy the Ancient portal. The plan is to put a new weapon, the meson bomb, into a decommissioned destroyed that fought the Great War, the Bastion, and replicate what happened when the Shivan first mothership exploded on its way to Sol. This should sever the access to the Nebula forever.
Escorting the flying 2-kilometers-long bomb to the portal proves to be a challenge as hostile forces keep coming in. Luckily, Juggernaughts are still away, and the Bastion warps in to the Nebula, while the meson bomb is activated. The shockwave blasts the Ancient structure as expected. As allies cheer in, Juggernaughts begin to warp in. The Ancient device made the wormhole extremely stable in a permanent fashion. In the following panic the blockading forces are wiped out. The crippled Colossus is sent in to save time. The crew of 35,000 sacrifices itself in order to allow other ships to escape.
Allies don't have time to mourn the losses. They have nothing left that can even slow down the Shivans and all they can do is to evacuate Capella populated planets and try to collapse another node (which ironically replicates the Ancients history). But the Shivans behave in a completely unexpected fashion, as they don't head for the next node. They head straight to the Capella Star and begin to orbit it. The Juggernaughts are so numerous they form some kind of Dyson sphere around the massive star. Each Juggernaught is equipped with 4 forward giant "claws" which were thought to be simply deadly beam weapons. It appears that the "claws" can be deployed and each ship begins to generate electrical arcs between their 4 claws, tearing the fabric of space-time and generating what look like singularities. Each ship generates its own singularity, and the Capella is surrounded by them. It causes the star to expand in a catastrophic fashion (as singularities - infinite gravity wells on a single point - "pull" evenly all around). At this points, the Shivan cut the power and the artificial gravity field vanishes. Capella's gravity is restored, and the star layers fall back as fast as they expanded. This causes an enormous compression which triggers a Supernova. At this point, a fraction of the Shivan fleet manages to warp through individual wormholes. Most of it is left behind and obliterated by the Supernova shockwave. Terrans and Vasudans continue to fight the Shivan rear-guard forces in order to allow the last civilians transports to evacuate. Some of them make it to the next node, others don't and are disintegrated by Capella.
The GTVA is safe again, but was completely unable to predict Shivans moves. It seems to be pure luck. Shivans were probably attracted by wormholes activity, as some animals detect heat or movement. Their first wave 40 years ago was only the military part of their move. Its only purpose was to clear the way for the "transports", the Juggernaughts holding their population. Their final purpose was to gain access to a star massive enough to deliver the required amount of energy in order to generate a link to another remote part of the Universe, or even another dimension. Their ultimate goal remains a mystery.
Terrans have to mourn terrible losses, but have learned a lot on wormholes. They can now hope to build their own portal, in order to stabilize the node leading to Sol, which was messed up by the first mothership destruction. They also have learned a lot on themselves, and know take as given that cooperation with others species is the only way to last.
