Q: the historian whose writings on the history of Oldtown were well regarded in his day. とはどういう意味ですか?
A: At the time, people thought the historian's writings (about Old town's history) were good.
Q: It illustrates why historians have assigned great importance to the issue of energy in the rise of the Industrial Revolution. とはどういう意味ですか?
A: More simply, this says:
“Historians believed that the issue energy was very important to the rise of the Industrial Revolution”

The “It illustrates why...” means that something (“it”) in the last sentence supports the information in this sentence.

To “assign great importance to something”basically means “to believe that something is important.” In this sentence, the issue of energy.

The “in” here refers to an event. “In” is often used for location and time, but can also be used for events.
Example: “The hero’s actions were important in defeating the villain.”
In this sentence, the “rise of the Industrial Revolution” is a historical event. The issue of energy was important in this event.
Q: ​‎But unlike historians ,they take on a time span of roughly half a million years とはどういう意味ですか?
A: 〜対処する
Q: putting your historian's hat on とはどういう意味ですか?
A: "Putting on A's hat" means, playing A's role for a moment.

"Putting on your historian's hat" means you think/act like what a historian would do for a moment.


Q: "Although historians 'are agreed' that the French Revolution started in 1789.."
is 'are agreed' correct? first time seeing it🤔
A: it might be grammatically okay but does sound a little awkward. Just "historians agree" sounds better
Q: what's an "historian" supposed to be?
A: a person who studies history
Q: what is as before?what is historian in this sentense!
A: Earhart disappeared 80 years ago. No one knows what happened. But ever since then, every few years, someone claims to have figured out what happened. And every time, other people point out problems in the supposed "solution." So it repeats and repeats and repeats. That's why this time, AGAIN, it's "so it was AGAIN." And that's why it's "as before" -- "as the last time," and "as the time before that," in fact, "as every time before." "As before," someone makes a claim. And "as before," just like the last time, someone else debunks it. Often, the people debunking the ideas are historians.
Q: An historian この表現は自然ですか?
A: It is old-fashioned, but correct, especially in British English.