What topic is relevant to both the colonial era and the age of reason?

In the United States, the colonial era (mid-to-late 15th century) and the age of reason (c. 18th century) are separated by by about 100 years, but they still have more in common than you might think. If you're looking for just one example, the most prominent is racism or feelings of white superiority.

When the colonists began to arrive in New England (c. 1620), they were surprised to find that the land was already occupied by various Native tribes. Because the lives of 16th century Native peoples was very different from what the colonists were familiar with and seemed primitive, they believed them to be inferior to white Europeans. For example, the tribes that were on good terms with the colonists frequently tried to help them acclimate to their new environment by offering advice on farming techniques. Because they believed they were superior, the colonists rarely took this advice and struggled considerably in the early years. More broadly, the belief that white people were superior to other races was an important influence on territorial expansion, particularly throughout the 19th century.

By the age of enlightenment, British colonists had established themselves in several parts of what is now the United States. Although many things had changed over the century, feelings of white superiority and racism remained an unfortunate aspect of most colonial cultures. Despite having formed trade agreements and friendly relationships with many of the Native peoples in their areas, many colonists still held a white supremacist perspective and viewed them as inferior. Additionally, by this time slavery was an important part of the economic structure in the North and the South, which was motivated by the belief that white people were superior.

While racism is a common aspect of both periods, it's important to note that the motivations were quite different. In the early years of colonization, the colonists were virtually unable to communicate with the Native peoples and that lack of communication made them seem even stranger to the Europeans. By the age of enlightenment, many Native people spoke English, as did the slaves. In colonial era, the racism was almost a byproduct of poor communication and misunderstanding. By the age of enlightenment, however, feelings of white superiority were more commonly used as a justification for the maltreatment of non-white people.