Re: Genghis Khan's armies accidentally invade Equestria.
Horses are incredibly valuable to the mongol society. Killing ponies would be like putting all your money on a pile and burning it.
Talking horses are probably less 'Ghengis Khan makes a military decision' and more 'Ghengis Khan calls up all his shamans, religious advisors and holy men and asks them what the hell'.
"We don't have to dream that we're important"