Most historians publish their work in books. So, for many topics in history, your best starting point is a good recent scholarly book. The easiest way to find that book is to ask someone else who is knowledgeable about your topic -- for example, your junior seminar instructor or spring JP advisor. But a thorough search of the library catalog is also essential. Here are some tips on finding books about historical topics in the Princeton University Library New Catalog.
Once you have a book in hand, read it. Alas, there are no shortcuts to this part of the research process.
While books are very important, historians also publish their work in articles in academic journals. And the easiest way to find journal articles is to search a bibliographic database that covers your topic: