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.
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.