First of all, the world-wide interconnection also called globalization is as high as it never was… so impacts in one (geographical) area, sometimes even small ones, could have influences on other areas or even much further. So actions and impacts spread much faster than information, knowledge and know-how which generates insecurity. In times with insecurity, investors move away from “riskier” investments into assets that are perceived secure - things like e.g. gold (which does not mean it is more secure than others).
As far as I know, no one has a crystall ball… therefore, one can only rely on history. Doing an analysis of similar incidents in the past shows that the impact on the stock market is rather small. The best we can do is rely on statistics and probability.