The following multi-subject databases cover a wide variety of subjects and are a good place to start looking for discussions of historical topics, including events surrounding the World Wars.
These specialized databases focus on more specific subject areas. They are good for finding treatment of specific topics related to the World Wars and analysis of those issues from the perspective of disciplines such as economics and political science.
Note: America: History & Life and Historical Abstracts allow you to limit your search to a specific historical period. Use the Advanced Search mode and scroll about halfway down the screen to enter a range of years (e.g. 1918 to 1939 for the years in between the world wars).
Below are a few selected resources on World War II and the Great Depression. These will be useful starting points for finding a topic or finding background information on a specific subject.