First of all, welcome to the study of history! It's a cool hobby, for cool people ^([citation needed])****.

The bad news is, you aren't going to get the exact answer you want right now. I'll explain why, and try to give you a sense of why you might have some misconceptions about what academic training in historical studies actually means in practice. The good news is, once you've recalibrated what you are looking for from your efforts to study the past, the whole thing is a hell of a lot less daunting.

First, to deal with your request: you will never, ever find sources that you can trust to be absolutely factual in their treatment of American history. By that I don't mean that all historians are inveterate liars, but rather that history past a certain point is not about facts. For one, even the most scrupulously honest and neutral historian needs to choose what facts to present to you, and these decisions will inevitably shape the understanding you take away from it. You mentioned Howard Zinn, who is an excellent example of a historian whose work tries to highlight this - by focusing on stories that don't make it into most American history books (such as by focusing on the development of the American labor movement), Zinn presents a narrative that is not necessarily less grounded in factual history (though there are plenty of legitimate criticisms of his precise treatment of events) but is nonetheless radically different than the narratives usually found in American history books. This reflects the reality that historians are always making subjective decisions - what questions they choose to ask, the sources they choose to focus on, the methods they use to analyse those sources and the narrative they build from that information. Two equally honest historians might make all these decisions differently, resulting in very different takes on the same topic.

This is actually not a bad thing! Our understandings of the past are not supposed to be static - the job of a historian is not to craft a single, definitive narrative of What Happened that stand for all time, but rather to take part in a process of pushing one another towards deeper understandings of how and why things happened the way they did. There's a common misconception that history is a pile of facts, and doing a degree in history is about learning as many of those facts as possible relating to your chosen area of expertise. Historical knowledge is then the ability to recount relevant facts in response to a particular question. What caused the First World War? Arms races, imperial expansion, nationalism, train timetables and whatever else you can grab from your bag of 'what caused World War One' facts. So long as you can tick all the relevant boxes in your exam answer, you'll get your marks and be accredited as an expert in the subject.

But, this isn't the only way to think about history education. If you meet someone with a degree (or multiple degrees) in history, their qualification is not necessarily having a larger pile of history facts to draw upon than other people (which has led to some profound disappointment from my teammates at pub trivia nights on occasion, but I digress). Rather, advanced training in history is more about teaching the processes required to build historical knowledge. You'll note that my 'answer' above to what caused the First World War was actually at least four answers - so which one is correct? Even if we allow that all of these factors played a role, how do we go about determining relative importance? History, as any historian will tell you, is less about facts than the interpretation of facts - how do we build explanations of what happened in the past from the limited evidence which survives? How do we go through that process I described above of crafting questions, choosing sources, applying methods and building narratives in a way that deepens our knowledge of the topic?

Where this leaves you as someone wanting to build your own historical knowledge is simple enough: just like someone embarking on a degree in history, you don't need to know everything to be good at this. Reading books that are flawed or not fully trustworthy isn't a waste of time, but rather an opportunity to think about why they are flawed, and to articulate the ways in which they might be better. Rather than trying to find one perfect book, read multiple imperfect ones, and try to trace the differences between them, the lines of agreement and disagreement that emerge. Over time, you'll find it more and more natural to evaluate historians' works on their own merits - what their exact claims are, and how well they've substantiated them. This is not necessarily a quick process, and the formal structures and training provided by a degree-level programme certainly makes it easier. But as numerous highly skilled, degree-less users here might attest, it's far from impossible to build these kinds of skills independently.