An archive of scholarly journals, this database includes a large set of history journals. Remember that it is an archive - articles published in 1950 may still be relevant, but they also may have been challenged/ made obsolete/ etc.
This is the list of databases that would be most likely to cover secondary scholarly sources. These may include different formats, such as books and journals. In some cases, you may come across a primary document has been republished in a scholarly source. Listed are only those sources across a broad array of history topics. Specific topics will require looking in other areas.
This broad database can be searched by cited reference (in other words, who has been using the seminal work you've found) and because of it's scope may provide more articles that are relevant to your topic. This is also useful for ancient history.