Peer-review is an evaluation process in which qualified individuals within specialized field of study reviews literature before it becomes published. This process helps keep standards held by the profession, improves the quality of work being published, and provides credibility & reliability to published work & authors publishing the work. The 3-minute video below describes and discusses the importance of peer-review and its process.
(NCSU video, 3 min.)
Example of setting the "Historical Period" in either of the history databases to focus on events between 1880 and 1930:
You have to make sure that you do not accidentally enter the BCE time span, when in fact your goal was to focus on the 20th century, "CE"