"be as easy as those of Ferdinando Cortez"

Ferdinando Cortez is Gulliver's naming of Hernan Cortes. While he is often now referred to as Hernán or Hernando Cortez ,in his time he called himself Hernando or Fernando Cortés . The names Hernán, Hernando and Fernando are all equally correct. The latter two were most commonly used during his lifetime, but the former shortened form has become common in both the Spanish and English languages in modern times, and is the name which many people know him by today. He conquered the Aztecs of Mexico who were not "naked Americans" but a highly developed civilization. However, they lacked horses and gunpowder. The Europeans, who had both, were able to conquer them with ease. It is this lack that rendered the Aztecs "naked" of any means of defense.

Gulliver discusses his difficult position because "whatever Lands are discovered by a Subject, belong to the Crown."  It was a long held view that if a citizen came across a land that heretofore was unknown, that citizen could claim the land for his homeland regardless of what the indigent peoples thought.