What does a journal written by frontier settlers most likely tell you about manifest destiny?

A journal written by frontier settlers would potentially give you insight into the thinking of individuals who were responsible of living out the philosophy of Manifest Destiny. These individuals were responsible for pushing the growth of the US westward and dealing with the uncertainties and dangers that these policies brought them. It would allow you to see whether these individuals were taking part in the westward expansion for political, economic, or other reasons.