Hi, this practice is called "periodization". Not discouraging others from responding here, but there have been a few lengthy posts on the subject that you may find interesting
Rules Roundtable #17: Periodization and Regionalization - introduction to the topic; hosted by /u/RioAbajo
Why do historians periodize history according to tool making technology (Stone, Bronze and Iron ages) and not agricultural/domestication advances? - general discussion, including links to other posts
Monday Methods|How does Periodization affect our perspective? - academic discussion; hosted by /u/Commustar
Let's Revolutionize Periodization - fun exercise; proposed by u/Tiako