I've said it before and I'll say it again...modern horses originated in the New World...migrated to the Old world...the New World population died out...no horse when Cortes appeared in the Aztec lands -poor Monty.
The Iroquois civ is a cultural HASH in civ3 and should be in...the plains indians or the iroquois aren't a civilisation by civ terms...the Spanish, Vikings or Ottomon would have been SO much better.
Especially in the context of a real world map and historic civ positions
http://forums.civfanatics.com/showth...&threadid=9842 where it ain't great if European civs trying to colonise America meet full-fledge civs.
A mod I'm going to have is one where there are no N.American civs but a hell of alot of barbarians there

More appropriate and then the horsies there don't matter so much.