For those who have the time, inclination, language proficiency (and attention span) to listen to a podcast in German: The history of systematic surveillance.
The thesis is that it was started in the mid-1600s when three conditions came together: For the first time, enough people knew how to read and write and there was actually something to systematically surveil: a great international culture of letter writing that had sprung up in recent decades. The starting point was the beheading of King Charles I of England in 1649. A huge shock to those in power. Suddenly all the other powerful European nations saw the need to better control their populace. The first to implement this was France which decreed that from now on all letters had to go through Paris, so they could be intercepted, opened and copied. With our recent experience of post 9/11 surveillance extensions it’s not hard to image what the pretext for this was. More security? Efficiency?
https://technische-aufklaerung.de/ta042-zur-geschichte-der-systematischen-ueberwachung/
In this context see also our mammoth timeline.