If someone has already done research on a topic you are investigating you are encouraged to seek out the same sources. Sometimes you may find an abundant amount of material that wasn't important to them, but is perfect for you. Other times you may find you disagree with their interpretation, which will give you something to write about from a fresh perspective.
Theses and dissertations are a great place to find bibliographies (sometimes called literature reviews) Many can be found in this database-
The library has many databases dealing with historical topics. Several databases contain primary source materials from various periods of history.Some of the best ones for research on a wide variety of historical topics include-