Start with these databases:
Multidisciplinary databases are extremely useful for finding articles published in interdisciplinary journals or in journals outiside of the discipline of American history that may still be relevant to your research topic.
In addition to containing journal articles, many of these database also provide citations for (or full-text access to) books, book chapters, dissertations, and conference proceedings, which allows you to cast a wider net in your effort to find sources.
Large Multidisciplinary Databases:
Other Multidisciplinary (Point of view) Databases: