Answer: The sentence that does NOT support the topic sentence is: "The Civil War was not a splendid little war."
Explanation: This sentence does not support the topic sentence because it contradicts the main idea that is being presented in the paragraph. The topic sentence states that the Spanish-American War was considered to be a "splendid little war" by many Americans, with the possible exception of the soldiers who fought in it. The rest of the paragraph elaborates on this idea, discussing why the war was seen in this way and how it was followed by the American public. However, the sentence "The Civil War was not a splendid little war" goes against this idea by suggesting that the Civil War, which was a completely different conflict, was not considered to be a "splendid little war." As a result, this sentence does not support the main idea being presented in the paragraph.