Thucydides can be interpreted as moralizing by telling a faithful version of the Peloponnesian War, rather than trying to distort it to fit his propaganda (not saying he did not do this, but his attempt is, at least on the surface, the former). His goal is history, not polemic, and is often a reference point as a "first" historian (Herodotus a more controversial precursor)*. To be a bit corny: if a story is being distorted for political purposes, then the truth of the story is likely also political. Thucydides did fill in some speeches, and recorded from memory, but at least according to him, he is trying to be as faithful to the sense of the speech as possible.

Today few historians directly try to "moralize" in their academic writing (which is frowned upon, afaik), but their work may carry inherent political weight to it. The British Marxist Historians are a great example (although a bit old). They have to be understood in the context of Stalinism (which they did not like), and strains of Marxist thought which, they argue, lead to Stalinism. While their academic work is a superb contribution, and not polemical, they were directly engaged in disputes with "structural Marxists" over Marxist theory of history (as well, of course, with the broader discourse in society, which is, as a rule, not Marxist).

For the British Marxist Historians, the Marxist interpretation of history means that social relations of exploitation yield class struggle, whereas, they argue, a structuralist Marxism tends to assume the existence of classes which end up in conflict. To put it crudely, the BMH view, class struggle is an emergent feature of individuals, and they charge that the Stalinist interpretation of history mechanizes history, and deprives the agency of working class (and ruling class) people, as simply conduits of historical development.

Thus their work targets subjects which aim to show how working class - and ruling class vis-a-vis their social relations of production - come to terms with their exploitation within their "cultural" context, and how this leads to class conflict. They want to emphasize this agency, to retreat from structuralist, mechanical arguments, especially as they became horrified by Stalinism and Soviet imperialism (ie in Hungary).

Their work then, not only aims to reframe history in general, but has an axe to grind with respect to Stalinists (or structural Marxists, more generally). Their arguments with structuralist arguments then contains a sort-of moral urgency, although again, their work is not polemic nor propaganda. The non-academic dimension to it is, however, unavoidable.

Other school's of history also have their political edges as well, although that I'm less aware of these. Thought this would be a useful example, to at least verify such a thing exists.

*John Lewis Gaddis - The Landscape of History; Van Den Akker - The Modern Idea of History

Harvey Kaye: British Marxist Historians