Author's Note: This story is being primarily written to both get rid of a few plot bunnies bouncing around in my head, and cure a case of selective writer's block I can't seem to get rid of. The premise is simple, this humanity is having a major internal cold war, leading to a truly absurd arms buildup. Their military-industrial complexes are similarly filled with power-gaming min-maxing antimatter-loving sociopaths. The final nail in the coffin is that this humanity is roughly 200 years "ahead of schedule". Also, I don't own mass effect (DISCLAIMER DISCLAIMER).

human derived power blocs

- Offspring of Stars (A society of post-scarcity gene-modded cybernetic transhumanists and their AI friends. They have extremely liberal policies and start owning everything further out than Uranus, along with Uranus itself and 25% of the asteroid belt.)

- Inner System Military Alliance [ISMA] (A coalition of separate states with a standard of living roughly equivalent to a 1st world country with the addition of self-driving cars and highly advanced medical care. They start out owning a terraformed Venus, Earth, Mars, and 35% of the asteroid belt. After they get FTL the acronym changes to Inter-Stellar Military Alliance.)

- Brotherhood of true Humanity (A highly religious polity that violently opposes any form of augmentation. They are extremely conservative on all matters except expansionism, and have launched 6 sleeper ships to Alpha Centauri, Tau Ceti, and other systems within 20 light-years 1 of them was launched to Arcturus. They start owning 40% of the asteroid belt, Jupiter, Saturn, and the associated moons thereof.)

1 week after the discovery of the Prothean ruins (2164, note that there have already been 4 major interplanetary wars by this point, but humanity is still confined to sol.)

[ISMA]

"So, this 'element zero' allows for FTL travel?"

"Yes, along with inertial dampeners and some other useful functions."

"Such as?"

"A functional reaction-less drive, for one."

"Anything else?"

"Their kinetic weapons could accelerate a slug to roughly 4,000 km/s with a 1 km accelerator, compared to our 500 km/s with a weapon of the same length."

"Impressive."

"You'd be surprised, the projectiles they used consisted only of 20 kg of inert iron/tungsten alloy."

"Seriously? That is pitiful. Our projectiles have a mass of 10 tons, 100 kg of which is anti-lithium, and they've got heavy armor in addition to a guidance system with 1,200 km/s of delta v."

"Also, this eezo allows for the creation of force fields to deflect incoming projectiles."

"Does it block energy weapons?"

"No."

"then those are useless, unless we combine it with our existing plasma sheaths to mitigate their weakness to kinetic weapons. Also make a variant that shoves the projectiles off to the side rather than wasting extra energy bringing them to a stop."

"Just 1 problem."

"What?"

"There's only enough eezo in sol to fit out 1 ship 100 meters long or less."

"Classify this as deep as you possibly can, and set to work on replicating the effect without this substance."

"Certainly sir."

2178

[OoS]

"We have discovered that the ISMA is working on a method of FTL."

"Explain the basics."

"Apparently it works by reducing the mass of both the ship, and the light near it. This means that light goes faster, and that it takes less energy to accelerate the ship than it normally would."

"Get to work on it immediately."

"Affirmative."

2196

[ISMA][OoS]

Much to the ISMA's chagrin both it and the OoS unveiled their first FTL capable ships within hours of each other. Also to the ISMA's chagrin was the fact that the one belonging to the OoS was bigger, and faster. Reluctantly, the 2 powers agreed to work together to keep this under wraps when it came to dealing with the BotH.

2203

[OoS]

The mostly synthetic OoS had decided to leverage the advantage this gave them by colonizing rogue planets, and using von neumann colonies in addition to cloning. When the BotH discovered that the OoS had colonized the rogue planet that had (in another timeline) been known as Tartarus, they immediately freaked and fired 100 superluminal missiles with a 160 teraton yield each at it (total boom: 16 petatons). Thus the gas giant briefly became a sun, blinding the OoS's sensors (and destroying 80% of their assets near Tartarus) long enough for the slightly slower BotH fleet (who had since stolen the mass-shifting technology from the ISMA, though they hadn't figured out its more... exotic applications yet) to arrive, finishing the job though they still took 76% casualties.

2234

The war between the OoS and BotH is brought to an end in the OoS's favor. The system Arcturus was too heavily fortified for the OoS to invade conventionally without taking unacceptable losses, and the OoS didn't want to cause unnecessary civilian death with interstellar missiles. The situation was defused by using the recently excavated Charon Relay (which the ISMA had told the OoS about to hopefully end the war before they got caught in the crossfire) to appear behind BotH lines and destroy most of the defensive assets in-system before return fire could be launched. Afterwards, the Relay is moved into interstellar space before being carefully disassembled and replicated over the next 68 years.

CASUALTIES: (OoS)

~8,900,000,000 individuals

~2,000 habitats

34 planetoids

~5,800 capital ships (5 km-15 km in length)

~42,000 cruisers (1 km-5 km in length)

~89,000 small craft ( 1 km in length)

(BotH)

~18,780,000,000 individuals

~4,300 habitats

3 planets (trope: earth-shattering kaboom)

~14,200 capital ships (3 km-10 km in length)

~68,000 cruisers (800 m-3 km in length)

~138,000 small craft (800 m in length)

2287

A dextro garden world with native inhabitants around WW2 levels (though significantly less militarized) is discovered by the ISMA. The planet in question isn't itself touched, but the inhabitants are notified that until they reach space the ISMA will gladly protect them.

2301

The OoS begins construction of its own Relay network, the devices they produce are both bigger than and inferior to a 'relic' Relay at 30 km in length, but they only have an effective travel range of 120 light years while being permanently linked with a 'partner' relay.

An ISMA colony ship goes rogue, its suspected location is roughly 12,300 light years core-ward of the main human sphere.

CENSUS: (OoS) (grabbing any systems it can, doesn't care if there's a garden world there or not)

~71,700,000,000 systems (not counting rogue planets, which effectively add another 100,000,000 system's worth)(4,100 ly diameter + 1500 ly height, assumed star denstity of 1 star / 250 cubic ly)

~212,000,000,000,000,000 individuals

(ISMA)

~83,100,000,000 systems (4,200 ly diameter, 1,500 ly height, assumed star density of 1 star / 250 cubic ly)(only 1 in 100 has a terraformable object)

~4,986,000,000,000,000,000 individuals

2342

17,000,000 self-replicating war machines invade the OoS. Before they can be destroyed they manage to devastate 23,000,000 systems. Upon analysis they came from wherever that rogue colony ship went.

2351

The OoS and ISMA launch a coordinated invasion of the revived BotH, which has expanded into a cylinder of space roughly 5,000 ly in diameter (assuming stellar and population density equal to ISMA)

2357

A BotH exploration/mining fleet (clocking in at around 3,000 fully armed warships) blunders its way into a Turian system, and launches a ground invasion after wiping out the local fleet.