There are two commercial article collections (from Ebsco and ProQuest) that try to cover all topics relevant to military studies. They offer scholarly articles, but also trade, popular and news magazine articles.
In addition, here are links to free military periodicals search engines from military libraries. The DTIC Online link in particular can provide access to other forms of information (reports, etc.)
And, to get to the complete lists of article databases (by subject) available here at Marquette, use the drop-down menu below.
Of the resources below, only two are 'traditional' library article databases: PAIS, and Worldwide Political Science Abstracts. The other databases will help you to find a variety of different types of sources, especially government documents.
Leadership is a subject that is very multidisciplinary, and gets coverage from many different points of view. But in practice, there are several disciplines that focus on it the most: business (management), and psychology. The databases below will get you into the scholarly literature for both of these fields.
This is an excellent 4-volume collection of seventy-nine articles by numerous authors, all republished from other sources. Although the four-volume set is only available in print, you can see the complete table of contents by clicking the title below. To find more books on this topic click on the categories under Subject in the bibliographic entry.