Answer :
Depending on the point of time during the Civil War or if this statement is from after the Civil War will affect the answer given. The Civil War showed that there was a need for a strong central government to maintain the Union because states could put up a legitimate struggle against the state if they disagreed with certain policies of the national government. Therefore, in the end it revealed that the national government was the sovereign power because the Union and the North won the war, however, early on in the conflict it showed that states and the national government were not able to make adequate decisions jointly.