The last few years had been a bit hectic for humanity: Lesbian mermaids, bimbos pandemics and invasions of squids gods. But what the humans did not know was the number of times they had been about to be occupied by extraterrestrial races obsessed with assimilating all the intelligent life of the galaxy.
One race in particular, the Lettuce People, came up with the idea of doubling humans into emotionless doubles and using them to grow more of their race and thus spread across the rest of the planet. So they landed on the outskirts of a small town in the American Midwest that nobody had ever heard of and began to turn all humans into green goo that later was collected and used as fertilizer. The townspeople were very rude to each other and barely knew each other so when they started to being impersonated by emotionless doubles they hardly noticed the difference. In the end a group of survivors realized that something strange was happening and tried to escape the city, but were unable to cope with the passive-aggressive behavior of the lettuce people and ended up lettuced. Thus, in less than a week all the humans in the area had turned into manure.
The government knew that something weird was happening but they thought that they were being invaded by Russians so they prepared invade the entire city and reduce everything to ashes. But before entering the town, the commanding officer ordered to his mens to take a nap so all the soldiers ended up like green goo as well.
Luckily a group of Martian filmmakers were passing through the area filming their next blockbuster "Flaming bovines". They observed these events with concern and, contemplating the uselessness of the American command, they decided to warn the command of their fleet that they decided to intervene in the best way they knew and destroyed all the lettuce people and people in just one night, before they spread to the rest of the world.
After that years of relative calm followed (ignoring the occasions when the hairless primates were on the verge of a nuclear war.) Everything was fine. Until the Cyberwomen Invasion of 1966.