Pretty much all of the horseless civilizations got rolled over by people with horses.

The quote wasn't that "no civilization existed without horses", it was that the horse was "decisive in shaping human history".

When you consider what happened to advanced civilizations like the Aztec and Inca when they interfaced with horseborne civilizations, the point makes sense, and isn't doing so by marginalizing people who didn't have horses.

Mongols are considered "western civilization?"

You seem to be inferring that I said that no non-western civilization ever used the horse?

I said no such thing.

I said that a great number of civilization and cultures, that lasted for many centuries, developed without ever using horses, and that therefore, the horse cannot be considered to define all of human civilization.

Domestication of the horse shaped human history pretty much everywhere except Africa and Southeast Asia.

And America(s) before the Europeans. And all the brillant cultures of the Pacific islands. Etc. So, really not "everywhere".

Yeah, but the Europeans showing up is part of history in the Americas. Thus, the horse influenced human history throughout most of the world. And the cultures of the pacific islands aren't really capable of proving or disproving any broad generalizations about human history. The pacific islands are separated from the mainland by thousands of miles and constitute a tiny land mass.

Also, the Americas till the Europeans showed up.

The Europeans showing up is part of history. And the horse is one of the things which gave Europeans a huge advantage over the native populations here. Hence, I, a descendant of Europeans, am writing this to you from the Americas.

Not nearly as much as germs and muskets.

Everyone has germs, but they wouldn't have had the muskets and more notably the boats to get here without the horse.

If it wasn't for germs and muskets, the Comanche would have conquered North America just like the Mongols conquered Eurasia.

One way in which horses shaped the world is precisely that they only existed in certain places: https://www.youtube.com/watch?v=wOmjnioNulo Absence vs. presence is an effect too!

"[H]uman history" is generally considered to be the sum, rather than the individual cultural parts.

For a non-Western chunk of data, see https://en.wikipedia.org/wiki/Horses_in_East_Asian_warfare

You're absolutely correct. The West is entirely evil, and non-Westerners are entirely good.

If I am misrepresenting your political philosophy, then you should say specifically what it is.