Explain how the Inca were able to unify their vast empire throughout portions of South America.

This is true about a dynasty.

A dynasty can be described as the sequence of rulers that come from a particular family.

This family is usually a very powerful one and what they do is to try to maintain their power and ruling for a considerable length of time.

It is also referred to as a hereditary monarchy. A series of rulers that come from the same family is what constitutes a dynasty.

Read more on dynasty here:

link