…individual survival in times of societal collapse is a very dubious benefit.

After reading Graeber and Wengrow’s The Dawn of Everything: A New History of Humanity (Allen Lane, 2021) I do feel that I have to make a distinction here. Seemingly, especially for ancient history, there are (see the authors’ lengthy discussion on the First Intermediate period in Ancient Egypt) times that were seen by later historians as a societal collapse, but that might not be experienced as such by the people actually living in those times. However, at least in Europe, throughout the Middle Ages, the legacy of the Roman Empire remained very much present in political thought, and was often seen almost as a Paradise lost in terms of political unity and acculturation. See  Peter Heather, The Restoration of Rome. Barbarian Popes and Imperial Pretenders, (Oxford University Press, 2013) but also the introduction to  Luciano Canfora,  Julius Caesar. The People’s Dictator, (Laterza, 1999; english translation: Edinburgh University Press, 2007); Walter Pohl (et al., eds.), Transformations of Romanness. Early Medieval Regions and Identities. (Walter de Gruyter GmbH, 2018); Julia Hell, The Conquest of Ruins. The Third Reich and the Fall of Rome, (The University of Chicago Press, 2019)

…inherent political instability provided a constant incentive for internal development.

 See Geoffrey Parker, The Military Revolution. Military Innovation and the Rise of the West 1500-1800 (Oxford University Press, 1988, 1999).

…West Berlin was never meant to resist any Soviet invasion attempt.

Fred M. Kaplan,  The Wiyards of Armageddon, (Simon and Schuster, 1983).

…New York City had some 18,000 fallout shelters

https://www.cnbc.com/2017/10/06/thinking-the-unthinkable-dont-rely-on-these-historic-fallout-shelters-in-case-of-a-nuclear-attack.html 

…nationwide economic disaster

Thomas Bishop, “‘The Struggle to Sell Survival’: Family Fallout Shelters and the Limits of Consumer Citizenship”, Modern American History (2019), 2, 117–138. 

…has started gaining a considerable support

Probably the first article on the Doomsday preppers was Evan Osnos’ New Yorker article “Doomsday Prep for the Super-Rich”: https://www.newyorker.com/magazine/2017/01/30/doomsday-prep-for-the-super-rich 

For a more extensive review of the topic, see Douglas Rushkoff, Survival of the Richest: Escape Fantasies of the Tech Billionaires, (W. W. Norton & Company, 2022). 

And also Beatrice Balducci, “Prepper Architecture”in Officina, 35, (Oct-Dec, 2021),  pp.10-17 (in Italian) also available online: https://www.officina-artec.com/project/officina-35/?fbclid=IwAR2XD-a1ns1_PHwHVKmgxzSGl-lMTkYXwwKB3tx-ztgC21SsIiQZ6qocG5A 

…Texas, Wyoming and Montana.

Srecko Horvat, Poetry from the Future: Why a Global Liberation Movement Is Our Civilisation's Last Chance (Allen Lane, 2019); https://www.forbes.com/sites/jimdobson/2017/06/10/the-shocking-doomsday-maps-of-the-world-and-the-billionaire-escape-plans/ 

…are equipped with armories, weapons and stacks of ammunition. 

See Evan Osnos, above.

…1970s survival manuals wrote, …

Cresson Kearny, Nuclear War Survival Skills, (Oak Ridge National Laboratory, 1979)

…global cooling is highly unlikely to occur within the next century or so.

and, according to NASA, even more: https://climate.nasa.gov/news/2915/the-atmosphere-getting-a-handle-on-carbon-dioxide/#:~:text=Carbon%20dioxide%20is%20a%20different,timescale%20of%20many%20human%20lives. 

…Niccolò Machiavelli

Quentin Skinner, Machiavelli: A Very Short Introduction, (Oxford University Press, 1981); Isaiah Berlin, The Originality of Machiavelli https://web.archive.org/web/20121202125009/http://berlin.wolf.ox.ac.uk/published_works/ac/machiavelli.pdf 

…hated by the people. 

Available free online at: https://standardebooks.org/ebooks/niccolo-machiavelli/the-prince/w-k-marriott