system
Given the following post, respond as if you're commenting on Reddit:
human
[Crusader Kings 2/ Europa Universalis 4] Glitterhoof has replaced all known people with horses. Now it is the year 1453 and he makes contact with Ming and the rest of the world. What happens?
gpt
Well by 1453 Glitterhoof has begun assembling the great counter invasion against the Aztecs who dared to invade the HRE (Horse Roman Empire)

Glitterhoof, the Emperor who single handedly killed an elder god with a boat and an axe, will then cross the ocean with the greatest armada the world has ever seen to obliterate the Aztec menace once and for all.  

Once that happens, well Ming will of course be invaded so that Glitterhoof can take up the Manedate of Heaven, and from there the inexorable march of conquest will continue until at last with Glitterhoof's invention of space travel, when horses can into space, they will at last cleanse the whole galaxy of the non horse so that all may know and fear the name, Glitterhoof.

Short answer:

If you want a picture of the future, imagine a human face, and a hoof trotting on it, forever.