Before Europeans, the largest beast of burden was the llama, and at best it could carry like a hundred pounds. This meant that for the long distance travel that the Inca engaged in, the primary transportation animal was Incas. Oxen, when combined with their plows, made it possible to bring more land under cultivation and also made transportation easier and more efficient, and plus European animals remade culture. The grossly stereotypical American Indian, like from the movies, riding the Great Plains with an eagle feather headdress and war paint, well he didn't exist before the Columbian Exchange because there were no horses for him to ride. And the introduction of horses allowed many Native Americans to abandon agriculture in favor of a nomadic lifestyle because riding around hunting buffalo made them far richer than farming ever had. Thanks Thought Bubble. But before animals and diseases completely reshaped the New World, it was New World plants that had the biggest effect on Eurasia.