If horses were never domesticated, the world would have been nothing alike the one we know now. The Indo-European invasions would have never happened without their use of their superweapon, the chariot.

I can't really imagine dogs pulling chariots, and wouldn't be nearly as fast as horses anyway. If horses didn't exist, the camel or dromedary maybe would eventually be domesticated for this purpose.

Slightly off topic: did the Indians (Mauryan empire and earlier) use horses? I know they used chariots and elephants but I never heard or read about Indian cavalry. Why not? They had neighbours that employed cavalry...