It all depends on who's affected and what the extent of the damage would be to said countries.
A big war right now would throw a large portion of the world into shambles for a while, and the longer it goes on the significantly more damaging it will be. As long as the internet is operating, Bitcoin will be able to proliferate, but there are so many individual variables that can affect whether or not Bitcoin would be good that it's next to impossible to determine either way.
A natural calamity or a disaster is one of an example that can decrease the Bitcoin's value. Depends on how many countries affected and where the disaster happens.
It could be a great loss towards people who will suffer on that time. There will be an absence of things needed in order to communicate with each other through social medias. But I know that people will find ways. We innovative anyways.
The nature of bitcoin is far different than rest of the regular currencies as well as other crypto currencies. In case any such thing happens, then this will then result in rise in the market value of the bitcoin as there will be chaos all over the world and that people will be looking for the ways which can then help them in staying safe from any such kind of thing to meet up their needs.