What set of conditions (technical or socio-economic) can crash blockchain or bitcoin to zero USD?
There are many conditions to crash any current market to zero, but in terms of cryptocurrency there are few:
1. WarOne doesn't simply recover from a massive destruction, whether by financial, stock or cryptocurrency all will suffer. Rebuilding what has been lost can be a painstaking task. Cooperation and trust are needed very much for any restructure but after a massive war it can be a very serious matter.
2. Network Failure If the main internet grid has been destroyed or any existing channels of internet has been replace by another technology it can disrupt the current market by shutting down P2P. No connection, No P2P.
3. Global Ban The current cryptocurrency market possess no potential threat on any fiat currencies but certain countries do ban any transaction in junction with crypto. If there would be a global ban regarding crypto markets and penalize those who engage such endeavors then most likely it will render the market into a crash.
Undoubtedly, all those options that you proposed can affect the cryptocurrency market and bring down the price of cryptocurrency below the usual level. But we must also take into account the fact that, for example, military operations can provoke the opposite effect, since fiat cryptocurrencies will no longer be valued and cryptocurrencies may take their place. It is under this option that many cryptocurrency users expect developments in relation to users from Iran, given the complex conflict between Iran and the United States. I think that the only and most important problem for cryptocurrency in the future may be weak stability in front of a quantum computer. As far as I know, even this problem is being solved by many experts today.