Well, the cart is a lot older than the bronze age. How about the taming dependent on the location of a certain resource (a grain)? I've read that the first war carts were pulled by cattle or oxen. Can you imagine? "Everyone charge!" *clop clop clop clop* The Celts, of course, had fast chariots when the Romans showed up. Without cavalry cover, I'll bet those Romans were pretty unhappy.

A warrior without his horse is.... a Viking?