Many libraries and organizations are making digital materials available online.
To find these collections, use this search string in Google or another search engine, in addition to keywords relevant to your topic, for example:
digital collection site:.edu "world war II" returning veterans
You can also try the same search limiting to site:org rather than site:edu BUT:
EDU = educational institution
In this era of "fake news," don't just trust the information you see on a website's "About Us" tab or page.
Questions to ask when you are assessing online primary-source collections:
Use Google and other sources to research the authors, organizations, or institutions responsible for the page and for its funding. Don't just trust the About page!
Every resource on this page is freely available EXCEPT for the resources in the box "Digital Primary Sources Available Through GSU Library" (right-hand column) which are available only to GSU students/faculty/staff.
These online collections include digital versions of many out-of-copyright works including government documents, historical magazines and other periodicals, and books published before 1923. Coverage can be spotty, but these sites are worth searching... just in case.