You may be asked to assess books on events in American history, and one way to do so is by reading published book reviews. Many journals publish reviews when books are released. Here are some tips for finding reviews:
In the search boxes at the top, enter the book title you are searching for and select "Title" from the dropdown list. America: History & Life does index three of the most popular sources for historical book reviews: American Historical Review, Journal of American History and Reviews in American History.
JSTOR and Project Muse also allow you to limit the results to book reviews only.