Read the excerpt from "A Quilt of a Country."

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 does the use of the term fault lines reveal about how the author views world wars?

She believes that world wars are necessary.
She believes that world wars divide Americans.
She believes that world wars are a small concern.
She believes that world wars are harmful to people.