The short answer is Traders.  Traders will use anything as an excuse to try and trade for profits.  Enough of them together move markets.  It is always temporary though, as wars these days aren't meant to be as destructive as in the past.  Typically countries have plans for how they'll rebuild an area before it is destroyed.  Countries these days will even tell the other country before they bomb them sometimes, to try and limit civilian casualties.  All this to just say that traders will cause volatility over anything they can, and war is a good excuse.