What a fascinating topic! I can help you find books, but I won't be able to recommend them, just show you how to find them using library subject headings.

Check out these subject headings:

Widowhood - History and just Widows are the two most key ones, then there are many sub topics you can hunt under Widows, such as Widows - Biography and then slap on some geographic and temporal terms to get things like Widows of the American Civil War. Worldcat will combine subject headings when it searches by subject, so you don't have to be exact. If you get very lost reduce your search to keyword (remove the su: in front of your words), but by searching subject headings directly, if you get the right terms, you can be very very precise, and it saves time spent sifting through irrelevancies.