This took me down an interesting rabbit hole. Thank you for that.

I think I understand part of your question inasmuch as you are asking why historical study seems to be colored so heavily one way or the other but rarely from the center. I may not have understood fully and I beg forgiveness on that.

I am a lowly bachelor's level historian who just took twice or more than the number of required classes to earn my degree because there were far too many topics I was interested in. Through that experience and my further study, I have some general opinions about this idea of bias.

I think that the period something is written in obviously defines what is being said. I don't think that is a highly controversial opinion. Different biographies covering Thaddeus Stevens for instance choose to focus on his abolitionist activities, development of free public education in his state, or battle with Johnson, all depending on the era in which the biography was written and the overall "agenda" of the historian.

I do think it can be controversial to argue that some historians have an agenda and use historical events and figures to shape current public opinion.

Sometimes current public opinion can shape how a historian views things as well. Zinn's "A People's History of the United States" is probably a good example of that.

I know that I never encountered a truly "pure" source in terms of simple fact in all of my study of history. Perhaps in the form of some kind of timeline that simply listed events, but even those are biased in the events that are included and the ones that are not.

As this article points out, historians detail past events, but always through the lens of personal experience and opinion. Historians as a group in my experience tend to hold stronger opinions in general than other groups so it makes sense that the material produced would be more polarized.

Ultimately, I think that is where the issue is. What you see as liberalism and then reaction to that is precisely that. I am not sure that anything can exist in between effectively or that it does. I certainly have not seen it. Study of history is largely looking at an event, or series of events, and interpreting them and forming a response of some kind. That response may be a narrative attempt but it will always be an argument for the point of view of the historian. I don't think you can avoid that.

The polarization that results is almost a natural product of the division that occurs within the culture of nearly everything. There is always an "us vs them" on every topic or within every ideology. I don't think the study of history is exempt from this.

Adding here that this is my first attempt to contribute to this sub and I may have done this wrong. I tried to cite some things but I may not have done it appropriately, etc. I am prepared for the smackdown if this is too opinion-based. It seemed like OP was looking for sources that I have not seen exist and I was trying to posit why they do not. It could be too speculative for this sub. Apologies ahead of time if so. It also could be that I completely misinterpreted the question in which case my answer is entirely irrelevant.

Liberalism is actually a difficult term, since it can mean so many distinct, and often conflicting, things. It can be a philosophical ideal or a political imperative, a synonym for progressivism or an ideology akin to Reaganomics, a defense of state interventionism or a plea for unrestricted markets. Classical liberalism, as I understand it—and this is certainly not my wheelhouse—is about individual freedom and minimal government.

Yes, that is a Wikipedia link, but I think this is as good a definition as any, since most depend upon a similar set of assumptions: individuals are the most basic elements of societies (rather than, e.g. families or tribes, or civilizations, religions, or anything else); freedom is an ultimate good and it is often implicitly understood in economic terms; and the way to measure freedom is by analyzing the relationship between the state and the individual.

So the development of classical liberalism privileged a certain set of terms for social analysis, including historical thought. The individual, freedom, and the state are at the center, but also included are things like economics, societies, politics, and even notions about which directions history should progress in or societies should evolve in.

These terms have proven to be powerful analytic tools, helping us understand the past and apply that understanding to present-day problems. They really didn't enter the historical vocabulary in force though until the early 1900s, with thinkers like Durkheim and Weber (gradually taking dominance over earlier cultural history). Historians then depended overwhelmingly on these terms until about the 1960s or 1970s, and the so-called cultural or linguistic turn, although intermittent debate over whether history should be classified with the humanities or with social science has ensured that the terms of classical liberalism remain the primary instruments for analysis in at least some parts of the field.

Given the diverse histories of liberalisms as well as their impacts on the historical discipline and institutions of historical study, it's very easy to classify all history-writing as either a derivative of classical liberalism or a reaction against it. However, I don't think this does justice to the variety and change that has occurred in historical studies since the Enlightenment—including the integration of scholars raised in non-Eurocentric milieux into the institutions of Western historical studies—nor does it acknowledge historians' continuing engagement with people who thought and acted before the Enlightenment.

There's lots of directions you could explore to see these alternatives, which are, however, rarely taught at Western institutions prior to graduate studies. As just a brief selection of possibilities for further reading:

• Ibn Khaldun, The Muqaddimah. This is an introduction to history, written by a North African scholar in 1377. It's thoroughly informed by Islamic traditions of historical thought, which were in many ways more elaborate that historical thought in pre-Enlightenment Europe, and which remain rich today. This is required reading for most serious students of Islamic history, and as the field of Islamic studies has blossomed in Western institutions since the 1970s, I think that Ibn Khaldun has been much more influential than Smith or Locke. (If you go for a copy, I'd recommend the abridged version; it's long enough, and the linked edition gets at the core of his thought.)

• Dipesh Chakrabarty, Provincializing Europe: Postcolonial Thought and Historical Difference (2000). Chakrabarty starts with your same observation—the European historical tradition developed out of Enlightenment thought. He portrays this as pervasive and in some cases pernicious. But Chakrabarty notes that not everyone is as bounded by European philosophical traditions as European philosophy itself asserts, i.e. not everyone is born into an implicit acceptance of the universals of European thought, such as capitalism and individualism, as their primary frames of reference. He offers a few ways of thinking outside the box of 'Europe' as a historical mindset, and he explains that doing so might help break the most pernicious and colonizing bits of 'Europe' apart as well.

• Jeffrey Jerome Cohen, "Midcolonial," introduction to Jeffrey Jerome Cohen (ed.), The Postcolonial Middle Ages, pp. 1-17. Enlightenment thinkers—following their Renaissance forebears—asserted the birth of a new philosophical era by inventing the term 'medieval' and classifying the Middle Ages as a time when people thought in different ways. This has made studies of the middle ages especially fruitful as a way for exploring alternatives to Enlightenment-influenced mindsets. Cohen's introduction is perhaps one of the better entry points to this discussion, although I'd also point you to John Dagenais and Margaret R. Greer, "Decolonizing the Middle Ages: Introduction"; Nadia R. Altschul, "Postcolonialism and the Study of the Middle Ages"; and Catherine Brown, "In the Middle." If you have access to a university account, your library should have these available online.

• Marnie Hughes-Warrington, Fifty Key Thinkers on History. This is a brilliant review of some of the most influential thinkers for modern historians, although certainly not all are modern historians. I'd especially point you to the chapters on Bede, Ibn Khaldun, Giambattista Vico, Leopold von Ranke, Jules Michelet, Michel Foucault, Hayden White, and Francis Fukuyama. Each chapter can be read during a quick sit-down, and each comes with enough bibliography that you can pursue whatever catches your interest. I think that almost anyone who has enough interest in history to visit this sub would probably enjoy reading at least parts of it.