 Complete the following phrase:  Naval power played a significant role during the American Civil War, in which the Union had a distinct advantage over the Confederacy on the seas. A Union blockade on all major ports shut down exports and the coastal trade, but blockade runners provided a thin lifeline. The Brown-water navy components of the U.S. navy control of the river systems made internal travel difficult for Confederates and easy for the Union. The war saw ironclad warships in combat for the first time at the 