The use of the words "would" and "could," along with punctuation, generally conveys a sense of possibility, speculation, and uncertainty. In the context of the given responses about racial equality in the United States after the Civil War, the most appropriate effect suggested by those words and punctuation is:
It builds the uncertainty that all Americans faced toward many elements of society after the Civil War.
This response captures the essence of how "would" and "could" evoke tentative thoughts and the indecisiveness present at that time regarding societal changes and racial equality.