I'm trying to find the source of the quote in the title.
This Guardian article from 2021 quotes ‘Hal Klepak, professor emeritus of history and strategy at the Royal Military College of Canada’ as saying:
As San Ignacio de Loyola, echoing the same conclusion as Machiavelli in such circumstances, said: ‘In a besieged city, all dissent is treason.’
I can't find any evidence of Machiavelli saying that line, but it may be that Klepak was paraphrasing his argument. However, I also can't find any evidence of San Ignacio (Saint Ignatius in English) saying that quote.
An online search for that exact quote returns: the Guardian article; a Havana Times article from 2013 that includes the quote in quotation marks but doesn't provide a source; and a bunch of content farms regurgitating the same Guardian article.
Searching for the phrase in Spanish also only yields a handful of results, which attribute it to Fidel Castro. Tweaking the wording (e.g., replacing ‘city’ with ‘fortress’) yields further hits attributing it to Castro, but usually saying he was quoting Ignacio (without providing a source).
Searching for ‘Castro’ alongside part of the phrase (back to English again) returns many more results, including claims that the line was a 1960s Cuban propaganda motto.
So did San Ignacio ever say this (or anything similar), or did Castro/the Cuban government invent the phrase and it later (intentionally or unintentionally) got misattributed to San Ignacio?