The correct option is: C. Both the Union and the Confederacy desired total authority by eliminating the other.
The main idea of this excerpt from Abraham Lincoln's Second Inaugural Address is that, four years prior, as he took office, the nation was on the brink of civil war. Despite efforts to prevent it and initial hopes of saving the Union without resorting to war, negotiations failed, and one party (implied to be the Confederacy) chose war to achieve its goals.
The passage reflects on the reluctance of both sides to engage in war but highlights that it became inevitable, leading to the Civil War. Therefore, the correct option is:C. Both the Union and the Confederacy desired total authority by eliminating the other.