So instead of re-creating the migrant fleet from Mass Effect. I'll go back to sorta my story I was deciding to go with anyway. I just won't try to re-create the migrant fleet, but it'll be a bit similar. Just not really the same as the one in ME.
Its the year 3018, and Earth only has 250 million people living on it. Up to the year 2851 there had been world war 3, world war 4 and the last war which lasted for over 200 years, world war 5. Earth has been turned into a mostly unhabitable planet (going to spacemaster terraform it), and most of the remaining population lives in the oceans. Animal and plant life on the surface had been driven to near extinction, with very little remaining. There also had still been racial wars, religious wars and most people had been ruled by dictators or corrupt governments.
However, during explorations of the deep seas (left uncharted for centuries), the year 2852 changed humanity. There they discovered remnants of a very ancient alien civilization, which united the remaining people of Earth. A brief war did follow to gain power, but a secretive religious group called The Covenant had formed around this alien tech. They quickly united the people of Earth (with some bloodshed) and gave humanity one goal. To leave the confines of the dead Earth, and find a new planet or solar system to call home. There, The Covenant suggested that to show that the human race was united, they were to construct a massive space station (making it a PDC, and less than 100 million tons, right now its 25 million) above Earth to act as a defense for those who may decide to stay, and as an historical landmark for centuries to come.
Skip ahead to present day, 3018. As the station nears completion, humanity sent scout ships to the various known bodies of Sol. What they found was a very large, powerful and thriving human population on Mars and various nearby moons. Way back in the early 2000s, some of the 1% of Earth, scientists and explorers had paid for travel to Mars. This was before World War 3 started, though not long before. Once the war started, Mars and the settlers there had long been forgotten and they were left to fend for themselves.
These "humans", who named themselves Martians (I know right, so cliche
), also had mutations from adaptation of living so long on Mars. Their skin is more red, and their ears are elongated, as well as longer and bigger noses.
These Martians however, not the friendliest people to Humans of Earth. War has not started, but there is much tension between the two species. Making The Covenant very worried of the future, and if they'll manage to migrate in time before the Martians enslave them. Though having such a powerful PDC in the orbit of Earth, as well as slightly advanced technology due to the ancient alien civ, may be the only thing preventing the Martians from declaring all out war.
So this game takes place on a pretty much dead Earth, with threat of Martians (long ago migrants to Mars from Earth) with a goal of leaving Sol and finding a suitable solar system to settle in.