Well the horses at least were quite intentionally traded, and I would be very surprised if chariots were not either, although admittedly, they spread mostly by

Well the horses at least were quite intentionally traded, and I would be very surprised if chariots were not either, although admittedly, they spread mostly by some poor saps being pounded to dust by the folks in chariots and then those poor saps adopting chariots themselves (e.g., the Egyptians and the Hyksos)