Question

Why is this letter an important primary source document?Which is the best source of historical evidence to learn about how an event unfolded?

Answer 1

Answer:

Generally speaking, letters are used as historical evidence or evidence in legal cases. Letters are written records of events and communication between people, so any information contained within is evidence of an event or interaction which happened.

The event could be unfolded when you utilize the best sources and books are major part in delivering it so.

This should identify with historical events so that it meets proper arrangement in reading historical events and best source is books.  

Otherwise newspaper account is also written when the event unfolded.