PhD dissertations are documents that are produced for a very specific purpose: to convince a committee that the author has acquired the skills necessary to be considered an original contributor to the scholarly field of history.

My joke to graduate students fretting over them is that they are just an elaborate form you are submitting. They do not need to be human-readable — just committee-readable! (And the committees do not always even read the whole things. I am reasonably certainly only one member of my committee read mine all the way through.)

Later, many of those dissertations are turned into books. Those are the things that are meant to be read by a more general public, and those also go through peer-review (a dissertation does not, except for the committee, but that is not really peer-review). Those also, incidentally, get edited for typos by a professional editor.

There are, of course, many dissertations that don't end up becoming books. Some of them are still quite useful and good. Additionally, some dissertations just are good reads and worth looking at on their own terms (those bastards).

But generally speaking I would not recommend reading dissertations. They are not really meant for human consumption. They contain sections that no idle reader in their right mind would want to read, like a long and tedious literature review.

You should think of them as drafts for a book by someone who is learning through the process of writing them. Some are still good. But you'd probably be better off reading the books that they turn into. If you find a dissertation on an interesting subject, Google the author and see if they turned it into a monograph. In virtually all cases, the monograph is probably better than the dissertation — it can't really help not being it, because it's often an edited, re-written version of the former by someone who has had a little more time to think about the topic and who is actually trying to write for an audience of more than three or four people.

The only people I regularly recommend read dissertations are graduate students anxious about dissertations, because that helps them jettison the idea that dissertations need to be perfect. But if you really want to, knock yourself out. Just be aware that the quality can vary significantly!