R&H and (eDTA) join forces.
A. Spanish conquistadors bring their horses with them across the Atlantic. Some horses escape or swim to shore after a ship sinks. The Plains Indians become expert horsemen and buffalo hunters.
This was certainly not intentional since hardly the conquistadors would want their enemies to be stronger.
B. B. Rats are aboard European ships coming to the Americas. The rats spread disease and hunt unknown numbers of smaller animals to extinction.
This is hardly intentional. Rats were almost unavoidable back then and the Europeans just did not care much about them. They weren't thinking about how the rats would cause trouble in the Americas. They were "just rats".
So the only intentional one is:
C. Columbus brought pigs to the Americas on his second voyage. The pigs provided a valuable source of food for a growing population.
Columbus brought pigs for them to serve as food eventually and so they did.
You need more information to support this; there are many things intertwined with the pure food and drug act
