I would say that the best answer would be the second option:
"To establish the goals and purposes of government."
A.) Tributary's were basically rivers and lakes. There were many significant battles on the tributary's. These also played a huge role becaused they helped get troops and other significant supplies across them
B.) Ironclads were steam powered warships covered by steel and much harder to destroy than the traditional wooden warship.
C.) Casualties are deaths, specifically in war. About 618,000 soldiers died in the Civil War. One of the most i the history of the wars in the United States. All these men (and some women) sacrificed everything for their freedom.