Some time into the future, mankind has been pushed to near its breaking point. Countless decades of war, famine, and pollution have taken their toll on the world, and it seems that all hope is lost. One day, an island/pocket universe known as Equestria, populated by technicolor horses, unicorns, and pegasi (all collectively known as “Ponies”); appears on the sea from out of nowhere. Unfortunately for humanity, Equestria is pushing into Earth’s territory through a magical dome known as “The Barrier”, and Equestrian magic is lethal to humans. Eventually, the Barrier will consume the world and kill off humanity.
To fix this, the Equestrian leader set up “Conversion Bureaus” all over the world, which turn humans into pony-like creatures known as Newfoals, which could go through the Barrier and live in Equestria. However, the ponification process has some noticeable drawbacks: the Newfoals are incapable of swearing or getting angry (or showing any other emotion besides happiness, for that matter), and their personalities are completely changed from what they were when they were human. At a meeting of the United Nations, Celestia (hereafter known as Xlestia) reveals her true intentions: she believes that all humans are inherently evil, so she intentionally teleported Equestria to Earth to convert all of Humanity and kill anyone who tries to oppose her. Mankind, who naturally sees this as Genocide, thus has no choice but to go to war against Equestria for its survival.
And so it went on infinitely many Earths and Equestrias across the Multiverse, with several variations here and there: an Earth Humanity invades Equestria, another where a second Equestria comes to Humanity’s aid, and even Earths where Equestria really did arrive by accident, et cetera, et cetera.
However, the stories we’re here to talk about focus on the failed attempts.
Have fun!