This sounds like a great project. Let me give you some ideas to get you started.
First, since this is a broad topic, you will have to narrow things down. You can choose one piece of literature that has affected you and write on that, or you can speak generally. Another idea would be to pick a theme and expand on it. There will be a great amount of flexibility. Hence, the point is that you need to narrow things down.
Second, if I were to write on a topic, I would write on the topic of religion and Christianity. Whenever I read older American literature, I see that there were many more references to the Bible and Christianity. This shows me that America in the past was a very religious country. It shaped their worldview and sentiments. Moreover, there was a certain assumption that people actually knew their biblical stories. The newer material lacks this biblical saturation. In many ways, it has been replaced by technology, the new religion, as I would argue.