Intellectual discussion: how would the global financial system collapse?

What do you think are roads to a total collapse of the international financial system?

Before we go into discussions, let’s first assume nuclear war or other extinction-like events won’t happen – people survive but the financial system is dead. And also there is no interference from aliens who do not intend to exterminate humanity.

Here are my guesses:
1. China and the US go to war, either direct or by proxy, before economic ties are severed properly.
2. The US banking system suffer from large scale hacks.
3. Coordinated actions by entities who hold large amounts of dollars – selling with the intention of crippling the dollar.
4. Total collapse of one or more large economy. For example, hacking and sabotaging of the electric grid of the US or of China that results in months of outage.

Feel free to post your ideas or critique mine.