While the horse was domesticated (and ridden) as early as 4,000 BC, it wasn't until 700 BC that the saddle was first used, and not until a few centuries later were stirrups invented.
What if the first horse riders (probably in the area of the Ukrainian steppe between the Dnieper and the Ural Rivers), or the Anatolian or Mesopotamian city-states they traded with, invented saddles and stirrups during the Copper or Bronze Ages? Any time between 3,000 BC and 2,000 BC. What if Uruk and Babylon and the Hittite Empire and Homeric Greece existed in a world where horseback riding was that much easier? Would it encourage earlier use of the recurve bow? Accelerated use of cavalry in battle (instead of charioteer formations)? Generally bigger and more mobile armies?
What if the first horse riders (probably in the area of the Ukrainian steppe between the Dnieper and the Ural Rivers), or the Anatolian or Mesopotamian city-states they traded with, invented saddles and stirrups during the Copper or Bronze Ages? Any time between 3,000 BC and 2,000 BC. What if Uruk and Babylon and the Hittite Empire and Homeric Greece existed in a world where horseback riding was that much easier? Would it encourage earlier use of the recurve bow? Accelerated use of cavalry in battle (instead of charioteer formations)? Generally bigger and more mobile armies?