Once these disparate parts were held together by a common enemy, by the fault lines of world wars and the electrified fence of communism. with the end of the cold war there was the creeping concern that without a focus for hatred and distrust, a sense of national identity would evaporate, that the left side of the hyphen—african-american, mexican-american, irish-american—would overwhelm the right. what is the denotative meaning of fault lines in this excerpt?