Chicago is the most common format for citations used in History papers.
Though there are several sub-types of Chicago, the most common form uses numbered footnotes. The exact format of the footnotes will depend on the type of source that you are citing, such as a book, journal article, newspaper article or archival source. Here is a generic example of a footnoted citation of a journal article:
The difficulty of citing properly is well-documented.[1]
[1]Smith, Bronwyn H. "Citations and Footnotes." Bibliography Quarterly (2005): 16-38.
