This historian would be using the skill of "comparative analysis," since he or she is comparing a wide variety of sources to draw a conclusion between them as a group.
The Olmec civilization was located in Mesoamerica, in a region that is now occupied mainly by Mexico. They were a very early civilization that came to prominence around the same time as Mesoamerica was flourishing.
William Henry Harrison was a whig, and ran for numerous political positions throughout his career. The loyalists were some of his worst political foes.
