Little did this band of trusting souls know that the population of this newest prospective member to the Intergalactic Association of Planets was not from here; that is, they came from another galaxy. They came, they invaded, they killed off all whose home it was and moved in, lock, stock and barrel. That was their mission. They were infectious and insidious. Moving from galaxy to galaxy, conquering all who opposed their rule, destroying everything in their path, showing no mercy. They called themselves humans.
A strange and wild breed, they believed their god had bestowed this mandate upon them, and they meant to follow it through. When the diplomatic mission representing the Association, a group composed of the highest ranking members, arrived, they would be shown all manner of courtesy and respect. It's how they worked. Smiling broadly, performing conciliatory rituals to assure one and all they were eager to belong to the IAP, convincing the mission members of their good faith and straightforward intentions, they would extoll the virtues of what they had to learn. They would then offer gifts to the mission with which to return home as proof of their sincerity.
However, the gifts contained viral ingredients undetectable by any type of force-oriented equipment. These humans were smart, crafty. Within days, posssibly one week, the entire central planet of the Association would be ill with an unknown disease, incurable, devastating, terminal. Other planets who came to help would fall into the same trap; no manner of protection would suffice. Within a month of the mission's return, the heart of the Association would be eliminated or at least reduced to manageable size. The humans had but to wait, pretending to be innocent, confused, wondering, troubled. All Earth occcupants had been inoculated, so invasion would be simple, a clean-up expedition at most.
Humans, the scourge of the universe.
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The scientists at the International Institute for Extra-Planetary Discovery (IIED) passed around tubes filled with strong herbs, making sure everybody's pipe remained full. They were in a celebrative mood and deservedly so. The one-millionth planet in the galaxy with sentient, intelligent life on it had just been discovered and contacted. A diplomatic mission was on its way to their average-sized planet this very minute. It would take three months to arrive at trans-quark speed. All were excited, even the administrator, a usually dour man who seldom even smiled. Life was good, bonuses would be huge, vacations would be granted to everyone involved in the actual contact. The planet they discovered was named Earth by its inhabitants.