Answer: something powerful and threatening
Step-by-step explanation:
A connotation is the meaning suggested by a word, including the emotions and associations that it comprises.
The literal definition of a fault line is a ground fracture caused by the movement of tectonic plates that could provoke an earthquake.
However, in this excerpt is used in its connotative meaning to describe the powerful and threatening wars and communist ideas that resembled a common enemy for different states, creating a feeling of national identity.