[seowulf]

I have to believe it was much before that.

I have read that horses were domesticated before that, but they were too small to carry riders for long distances. They were better for pulling carts and packs, so chariots were used in war. It took a while to breed larger riding horses.

[Mr. Blond]

The Yamnaya developed the wheel due to their geography, and are quite renowned for their war-wagons which helped them sweep through Europe, and then back to the Indus valley.

[blam]

War Of The Heavenly Horses

"Blood-sweating" Horse Sparks Chinese Equestrian Interest

Pants were not invented until people began horse back riding:

These Are the World's Oldest Pants

"Jeans may have been invented in 1873, but these trousers beat that date by a long shot. A pair of wool pants was recently discovered in a graveyard in western China’s Tarim Basin dating back to around 3,300 years ago. They’re the oldest pants archaeologists have ever found—though they look like they might fit in quite well at Anthropology."