"When two banks transfer money, there's no concrete thing being moved or transmitted. It pretty much just involves bank B telling bank A "You hereby have $100k

"When two banks transfer money, there's no concrete thing being moved or transmitted. It pretty much just involves bank B telling bank A "You hereby have $100k of my cash". So A needs some kind of global ledger to keep track of how much cash B actually has, and double check whether it's already told C, D, E that they have all of it." No, there's no global ledger, and it isn't required. There are checks and balances and regulations that allow money to work in a completely distributed way. Unlike cryptocurrencies that use a centralized ledger (all the 'major' ones, at least).