where would a text like the American declaration of independence be placed? (which I'd say is an essay but I guess also a historical document. is there a category for historical documents anyway?)
973.313 for the declaration of independence
Not every historical document has its own categorization, but American history is especially fleshed out in the dewey decimal system. In general, I'd look for specific documents under their respective countries in the 900s section, history/geography.