The correct answer to this open question is the following.
Unfortunately, you did not mention the title of the book/article/text. You did not include the name of the author. So we do not know who the author is either the name of the story.
However, trying to help you we can comment on the following.
The literary device the author is using in this line, "White terror is as American as the Stars and Stripes" is a metaphor.
We know that in grammar, a metaphor is a figure of speech that the writer uses to make comparisons. The way the comparison is written is not literally true but really helps to make a point.
In this case, when using the phrase "White terror is as American as the Stars and Stripes," the author hoped to accomplish the following idea. That white terror is so ingrained in the American culture that it is an intrinsic part of American society.
We do not know the context of the phrase because you forgot to mention it, but there, alone, the phrase compares terror as racial segregation and division in the American society, meaning that is something common, that happens on any given day, as we can witness by the many past and recent events regarding police brutality against black people.
