American literature  is one that was written or produced in the United States and its preceding colonies
American literature is literature written or produced in the United States and its preceding colonies
That is very true my friend,  British life had a big influence on the way literature was before American came into existence
yes, and also the American literary tradition thus began as part of the broader tradition of English literature.
We can see that most of American styles are actually intertwined with British 
American Literature has been regarded since its inception as the preeminent periodical in its field
Do you know what the occupation of Thomas Jefferson was?