This is, of course, a question that can only be thoroughly answered through a large number of books. There are many aspects to the historical geography of the Americas. All we can do here is to touch on some of the most important of these aspects.
First, we can say that the Americas were not originally “the Americas.” In other words, in terms of historical geography, there have not always been “North America,” “Central America,” and “South America.” Instead, the areas that we now call the Americas were once simply one large area that was divided up into the domains of different tribes and nations. This did not start to change until the coming of the Europeans.
Second, we can say that the Americas were once divided up largely on the basis of who had colonized them. During colonial times, it was best to speak of Spanish America, French America, and British America. These were more relevant terms than the more geographically oriented terms we now use.
Finally, we can say that there has come to be a divide between the United States and Canada one the one hand, and all the other countries of the Americas on the other. This divide has been growing at least since the time of the American Revolution. It is now an important divide that separates the Americas in linguistic and economic terms.