The connotative meaning of fault lines in this excerpt is something powerful and threatening.
A fault line is a break in the Earth's surface. It is mainly used to talk about a crack that occurs when the Earth's tectonic plates move or shift. In this excerpt in particular, "fault line" has been used in a metaphorical way to refer to the power that world wars have to create a fracture between nations and the power they have to bring destruction. In that way, "fault lines" has a negative connotative meaning in this excerpt, which means that unpleasant emotions are associated to that word. Moreover, wars are also conceived as something negative in these lines.