What is the Communciation speed of ATM to all other ATM's in the world?
How atm communicates to all the atms in the world, hey, from this next millisecond his account balance is minus current draw?
CAP theorem gives the database of money transfers the ability to be consistent, partition tolerant, or available. Pick 2. All banks choose consistency, they have to. And partition tolerant is the obvious second choice so you don't magically lose all you money during a server crash.
If you're thinking someone can withdraw money in one country and do the same in another country would it figure out the correct balance or could you trick it? The answer is you cannot trick the ATM.