History books aren't quiet about Spain at all. High school textbooks might be, but not history books.
I've written a larger post on why Spain didn't enter WWII here, where I also detail a little bit about La Division Azul. I am very open to answer any follow-up questions. :)
hi! I'll leave Bernardito with WWII, but fyi you'll find some info on Spain in WWI in these posts
Why wasn't Spain more involved in the World Wars (particularly WWI)? - includes a link to the FAQ if you're interested in more on neutral countries in WWII
In WW2 Spain was home to lots of espionage work, and lots of money was effectively pumped into Spain by both the Axis and Allies secret services towards this. In Cadiz, a German Abwehr agent got hold of documents found on a deceased British serviceman which were held by Spain on behalf of Britain. These documents suggested an allied landing in Greece instead of Sicily in '43, a deception which was part of Operation Mincemeat, a British intelligence sheme. Certainly Spain was host to lots of such intelligence and espionage work, despite its non-belligerent status.