According to Guns, Germs, and Steel, why did Europeans conquer the Americas instead of Americans conquering Europe?

In
Chapter 3 of ,explains why the Europeans were able to conquer the Americas
rather than the other way around. He begins the chapter with a close analysis ofFrancisco
Pizarro's defeat of the Inca King Atahuallpa in 1532, despite the Spanish forces being vastly
outnumbered.

The first element underlying Pizarro's victory was superior
military technology. This included the use of horses, guns, and steel swords and shields, which
not only were vastly more effective than Inca weaponry but also terrified many opponents.

Just as important as military technology was the spread of European
diseases such as smallpox, typhoid, and...