History is the study of past events, particularly macro events. It's a broad category of things, and it absolutely can create theories. What subject of intellectual inquiry doesn't have theories? It's not a subject if it has no theories, it's a fact, or a collection of facts, which history most definitely is not. Historians are absolutely qualified to talk about humanity's development, same as biologists. Creating harsh divides between subject matter is ridiculous- there are many ways to look at the idea of human history, and a lot that any particularly style of inquiry can extract- and make no mistake, the "subjects" as they're divided in grade school are just different inquiries about the same problems. Math included, before anyone thinks I've forgotten about it.Documents can suggest, imply etc but they can not prove causality.
I think that this is deeply flawed. Nothing, at root, can prove causality, but the agreement we've come to is that a common understanding of past iterations of something does imply causality, until an event should disprove it.