Need help thinking of an essay topic. Prompt is to find a common theme within American literature (authors below) and compare two texts in the...

There are a lot of themes present in American literature.  For your prompt, I recommend staying fairly broad in your theme choice.  That will give you a lot of "wiggle" room to choose different authors.  You want that, because the list of authors that you provided spans hundreds of years worth of American literature.  

I would have a strong desire to pick a theme related to nature and the importance of nature to American...

There are a lot of themes present in American literature.  For your prompt, I recommend staying fairly broad in your theme choice.  That will give you a lot of "wiggle" room to choose different authors.  You want that, because the list of authors that you provided spans hundreds of years worth of American literature.  

I would have a strong desire to pick a theme related to nature and the importance of nature to American authors and their stories.  That would allow you to use Bradford's Plymouth Plantation. More importantly though, it allows you use any of the romantic and transcendentalist authors that are listed there.  Irving would top my list, because some of his descriptions of nature in "Rip Van Winkle" are gorgeous.  Emerson and Thoreau are good choices too, but I find them dry reads.  Lastly, you could use the early Native American literature that you listed.  Their entire society and religion is based on a harmonious relationship with nature. 

A different theme would be the importance of logical thought.  For that you could compare writings of Paine, Jefferson, and Franklin.  

There is a lot that you could do with Poe and Hawthorne too.  Both authors tend to thematically focus on death, revenge, and guilt.  What might be nice for you regarding those two authors is that they wrote a lot of short stories on those themes, so you could have a lot of different examples.  You might be able to work in some Dickinson stuff here too.  She has a lot of poems about death. 

You could focus on a theme of God and religion.  Bradstreet and Bradford are great for that.  Their Puritan values are always at the forefront of their writing.