It's not just energy though. You're talking about a whole globally interconnected extraordinarily complex logistics chain. If a market collapses or there's an ecological catastrophe in someplace like Brazil it can end up fucking Japan and Australia, which in turn creates a domino effect of fucking everybody else. Quite frankly I'm surprised it has even lasted this long. I mean just think about it, even the little things you would never even think to concern yourself about like C02 supplies in the culinary industry. UK and EU just got fucked by a shortage. These things don't just come out of thin air. You have a large complex creating and servicing all these different aspects which is made even worse by dumb shit like how chickens will be raised in one country and shipped all the way across the planet to be slaughtered there before getting shipped to another country as food.
I think the biggest threat remains plague though. It has killed off entire human civilizations repeatedly. The antibiotic resistant ones are terrifying. I'd say it'd only take one really good flu virus or ancient now dethawed bacterial pathogen etc to do the 2019 World Tour and it would not only kill off untold millions in its own right but would also manage to crash the global economy. The problem is, these things can have a cascading effect, so things such as crippling the infrastructure and logistics of dense urban centers will act as a force multiplier, override the surge capacity of all hospitals, and even without the social panic will start digging into food, medical, sanitation, and other basic supplies and services upon which the very hourly existence of dense metroplexes depends.
I mean look at Syria. One of the biggest problems was just modern siege tactics. If you so much as took out several highways and rail installations it would cripple and starve NYC ameliorated only by port, all of which is going to be a problem if you have a biohazard quarantine due to some plague. But honestly one of the worst things to me is how these idiots initiated the global dark ages unwittingly by burning all their hard copies while transferring everything to digital. Just think how hard it is to retrieve certain bits of data that were originally stored back in say 1991. Now imagine trying to retrieve that data in 2081. Hell just imagine all the data that was stored to punchcards in the era of OP's pics that either doesn't exist anymore or there's nothing left to read it.