Question

How is organizing the past by theme different from organizing the past by region?

Answer 1

 A historian who organizes the past by region focuses on a specific start and end date, whereas a historian who organizes the past by period focuses on the most influential individuals" would be the best option from the list, but in reality historians who focus on a specific period take into account many different factors of life during that period. 

Answer 2

A historian who organizes the past by region focuses on a specific start and end date, whereas a historian who organizes the past by theme studies a specific civilization. You can study, for example the period during the world war I, or the 5 years that preceded it. On the other hand, by theme, you can study Nazism.