Okay, this is just an idea that I thought of while trying to guess what the plot would be for an ME4 game (and even if Bioware should do it). I love Mass Effect, but now it seems Bioware/EA is just trying to milk the series. Shepard was the key character. It just isn't Mass Effect without him/her. I think that Bioware should take a new direction. I am currently in the process of writing my crossover Collapsing Empires so this won't be worked on for a long time. This is just an idea based upon this premise: What if humanity discovered the Citadel First? What if humans were the most advanced species in the galaxy? What if they weren't united under one banner? This is just my fun interpretation.
1 billion B.C.E. – An unknown race discovers element zero. They build the mass relays and the Citadel as the pinnacle of their power.
500 million B.C.E. – This unknown race destroys themselves in a civil war, leaving the galaxy a lifeless husk. Life would not return for millions of years.
8,000 B.C.E. – Humans start to rise on a world they call earth.
2,148 C.E. – Humans discover ruins of an ancient civilization on Mars. They discover the science of mass effect technologies.
2,149 C.E. – Humans discover the mass relay hidden in Charon and deploy multiple colony ships through the relay. The Systems Alliance is established as the arching government of humanity.
2,155 C.E. – Humans establish their first wave of colonies along several worlds. They discover more mass relays, the most important being the Arcturus Relay.
2,171 C.E. – Humans discover the Citadel and move to make the Citadel the capital of the Systems Alliance. Second wave of colony ships is sent out.
2,193 C.E. – Waves of protestors in the colonies start to call out for independence. Alliance Parliament tries to solidify their power as the authority for all humans.
2,195 C.E. – The First Rebellions begin with the assassination of the Prime Minister. Civil war engulfs all of human space.
2,227 C.E. – The First Rebellion ends with the Systems Alliance in tatters. Several governments have gained their independence from the Systems Alliance. The most important nations being the Republic of Terra Nova, the Red Star Union, the Greater Reich, the Alpha Centauri Federation, and Earth, which had become the Terra Firma Empire. The Systems Alliance maintained the Citadel, technological edge and most of human space, but was in a poor state.
2,238 C.E. – First Contact with the Protheans. Biology of the Protheans to see and feel thoughts through touch proved to be critical for peaceful contact. The Prothean Empire is very small compared to the human nations, but they prove to be a very powerful presence. Their philosophy of the Cosmic Imperative makes several nations nervous. The Omega Station is discovered.
2,272 C.E. – The Second Rebellion begins with the colony of Shanxi declaring its independence. The other independent nations get involved and infighting starts to destroy the human nations.
2,281 C.E. – The Protheans, seeing their chance, attack the human nations. They had hopes to secure their dominance in the galaxy to prove the cosmic imperative. In response, several nations band together to fight the Protheans while others declared neutrality. Contact with the Asari is made and proves to be peaceful.
2,294 C.E. – The human alliance shatters the Prothean Empire. The Protheans stay united, but must pay extreme reparations for their attacks. The humans are very interested in their biotic abilities and work to see how humans can gain them. The Asari demonstrate natural biotic ability, which makes humans even more determined to gain the ability for themselves.
2,295 C.E. – The Second Rebellion ends with all of human space shattered into competing nation and empires. New on the galactic scene is the Tau Ceti Sector Authority, the Geneva Confederacy, the Omega Federal Republic and the many independent colonies between these major powers. The Systems Alliance has officially been shattered, with only the Citadel to call home. They reform into the Citadel Council and try to act as a United Nations, but fail many times.
2,299 C.E. – Contact is made with the Salarians and the Quarians. Both hold the "human empire" with both awe and contempt.
2,305 C.E. – Contact is made with the Batarians. War breaks out, resulting in the Batarians confined to their home system. Piracy starts to plague the galaxy. Whether it is by freelancers or by financed by rival nations is unknown. The Salarians begin to observe the Krogan and the Rachni, seeing them as potential pawns to use against the humans.
2,306 C.E. – The Asari encounter the Elcor and make the Elcor a protectorate race, fearful of what could happen if they contacted the humans first.
2,309 C.E. – First Contact with the Turians and the Volus end in a war for the independent colony of Shanxi. They call upon their allies. The war is ground to a halt as the Turians had an efficient military while the humans had been divided with infighting.
2,312 C.E. – A peace agreement is arranged between the warring nations, though relations still remain hot. The Asari start to try and bridge alliance between all the different races. They are successful with the Salarians, but are rebuked by the Protheans and Quarians. The Quarians start to work on their drone workers, known as the Geth.
2,320 C.E. – The Citadel Council, trying to gain more authority over the distant human factions, creates Cerberus, a black ops group dedicated to fighting threats throughout human and alien space. Run by the Illusive Man, Cerberus recruits their newest member, Shepard, a hero during the Turian War.
After all this, Shepard would find an artifact/evidence of an extragalactic threat that would destroy all of the nations. In order to combat this threat, Sheaprd would have to unite the galaxy in some way, for only the combined might could hope to win. Now, the choices would work like this: You can choose to unite human factions with each other, but those choices would eventually alienate all other races in the galaxy. Humans would be too dominate and conflicts would break out. If you choose to unite all of the races, then you essentially leave the human nations hanging and they would eventually go to war. During this war, the other races would ascend and assume the post of the Citadel Council, effectively achieving peace but at the expense of a war with whatever human government is left. This is just an idea. If you want to adopt it, then just PM me.