A historian plays an important role in writing history. mention two roles
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The primary role of a historian is to inform others, and to accomplish that task, the historian must be a narratoAt its most simple, the role of the historian is to read records like this, report on what he or she finds there, and thus inform the wider world about the past. The most basic forms of history might cease at this point -

Explanation:

in 1897, pershing became a tactical officer at west point, and that's where he was given the nickname "black jack." pershing's first name is "john," for which "jack" is a nickname, and he was a white man who commanded black troops. hence "black jack".

porter is writing economic history because he is focusing on the cost of developing vaccines.