AFIP selected.A) For their own reasons, they started with the lightest forces and increased the pressure over time, until we broke.
F) Violent psychic ferrets. They're interested in conquest and war.
I) Soldiers, to be thrown into a war.
P) Slaves.
They call themselves the Zhuul. They live for conflict, even in - perhaps because of - the ravenous pre-sentient childhood stage of their lifecycle. Such a species can only thrive on the backs of their slaves, and so they came to Earth. How long will it even last under their rule, before being left a barren husk?
The first wave brought devastation, but we eventually managed to cull the hordes of their young their slavers leave behind. We managed to down one of their abduction saucers, and at great cost, wear down and eliminate the crew.
Their technology is ramshackle, and surprisingly ugly for a spacefairing species. Still, it was enough to reverse-engineer fusion reactors and fusion jet drives.
By the third wave, we could actually retaliate. A trio of converted submarines hidden in orbit, loaded with box launchers and prototype fusion missiles, were able to cripple their flagship before being destroyed. In an apparent coup, the Zhuul finished destroying the flagship themselves, and proceeded to bomb our major cities and military centers in retaliation. (Previously they had ignored our defenses and focused on taking slaves.)
We were devastated, but things had changed. We hadn't earned their respect: The Zhuul have none to give. What we had done was proven that we had potential to be useful to them.
The Zhuul consider Humanity to have
one big advantage that sets it apart on the field of warfare. What is it?
A) We're highly resistant to psychic powers. Some of us manage to be impossible to sense. This comes at the cost that we will never be able to wield these powers ourselves.
B) Organization. The Zhuul fight in small packs, each seeking joy in slaughter. This tendency restricts even their best ground commanders. Humans manage to be more communal than most of the Zhuul's rivals, easily creating and following chains of command and ignoring personal objectives.
C) Stamina. The Zhuul are terrifying foes in combat, all claws and psionic fury. But this comes in a burst, and they have serious trouble fighting on-and-off battles spanning a week. World War 1 trench warfare is absurd to the average Zhuul.
D) Science and engineering. X-COM BABY ALL DAY E'ERY DAY!
Who are we?
E) We lead one of the first marine companies conscripted by the Zhuul. Ship-to-ship battles aren't to our strengths, but taking and holding hostile planets are.
F) We'll be placed in charge of a new frontier fortress and responsible for protecting the planet. The planet has an ork infestation, which can outfight standard Zhuul garrisons. The native Zhuul are unlikely to accept our gonvernorship, and we are expected to constantly be in low-level combat them as well.
G) We were the ground-side admiral in charge of the sucessful space-submarine strike. To see what else we can do, we will be granted command over a small outdated fleet, based at Earth. Zhuul marines will be aboard all ships and only nominally under our command, ensuring our obedience.
H) We can never accept Zhuul overlords. We're in charge of a resistance cell on Earth, and will fight on.
1) We fight for vengeance.
2) We fight for freedom.
I) We will be in charge of a group allowed to attempt to colonize a former Zhuul world stripped barren. They'll demand tithes, likely before we're ready for them.