Read the excerpt from "A History of Voting Rights.” In 1870, the Fifteenth Amendment to the Constitution became law. The amendment established that the right of citizens of the United States to vote could not be denied by the United States or by any state on account of race, color, or previous condition of servitude.

Which aspect of historical context does this excerpt describe?

a development in world events
a change in society and its values
a development in technology
a change in national politics