At the time, the number of soldiers killed during the Civil War:
D) was more than the number killed in all previous US wars combined.
American military deaths during the Revolutionary War totaled around 25,000. The death toll from the War of 1812 = around 20,000. The Mexican-American War (fought about 2 decades prior to the Civil War) left around 13,000 American soldiers dead. So all together, that was less than 100,000 killed in those wars. In the US Civil War, over 600,000 soldiers were killed. The Civil War saw more American deaths than any other war in US history, including World War II. (Around 400,000 American military personnel died in that massive conflict.)