Answer:
There were vast differences between American societies and European societies of the late 15th century.
Step-by-step explanation:
First of all, the European societies were far more advanced, technologically speaking. The Spanish and the Portuguese, the first European nations to contact the Native Americans in this period, had access to gunfire, horses, iron, the compass, powder, and large ships, and this allowed them to defeat not only small tribes, but large empires like the Aztec and Inca Empire as well.
The Native Americans had some technological advances of their own, but at least military-wise, they were no match for Spain or Portugal. The American populations also suffered greatly from the lack of immunity to diseases such as typhus and measles, which were brought by the Europeans, and killed millions of Native Americans.