Why do you think so few animals diffused from the Americas to Europe

The Europe is diffused the few animal of american because the Europe was trying to expand their country because of the over population Russia expand it to the new world.

Explanation:

So they kept the source of the animals such as food, shed, in the america to support the growing population of the Russia.

Because the animal causes the disturbance for the newer world. and the long voyage taken by the nomads over the seas the animals would have been difficult for them to survive in unsuitable areas. Animals are took lot of space in the newer world so the Russia diffused to kept the animal with them.