One year into PhD, feeling lost and inadequate, Help!

This is the reason you gave for pursuing a PhD:

 I hated working on my master's thesis, but I nonetheless grabbed the opportunity to start a PhD, because I convinced myself that it was something that I would be good at, I wanted to overcome my anxiety and challenge myself mentally, and the stipend is very decent.

You don't say that you were anxious about writing the thesis, you say that you hated it, which sounds to me like you simply don't like doing academic research. But that is the whole point of a PhD. Furthermore, the only career a PhD in history really prepares you for is research and teaching, and you don't say anything about your feelings about teaching.

So it sounds like you enrolled because of extraneous expectations from both yourself and others. Getting a PhD is not a merit badge, it's very specific training for a very specific purpose. There are plenty of other ways to show that you are smart. And "losing" one year is no big deal, especially when compared to spending even more time going down what might well not be the right path for you.