That's an excellent question. A full-scale nuclear war would disrupt the Bitcoin blockchain so badly, that only a small number of nodes and miners will remain online. By that time, people will be thinking on how to survive instead of hoarding currencies or investing in risky assets such as Bitcoin or Gold. Why would you care about Bitcoin when humanity would be at the risk of extinction?
I'd say a nuclear war would be inevitable due to rising geopolitical tensions all around the world. There are many countries with a huge nuclear arsenal at their disposal, ready to fire at will. When will that happen (WW3?) is an excellent question. I just hope the conflict between Ukraine and Russia comes to an end, otherwise things will only get worse in the long run. Who knows if there's a dark future ahead of us? Just my thoughts
