 The Civil War refocused discussions about the road . There were fears that Great Britain would enter on the side of the Confederacy during the early days of the war . British troops were as close to Michigan as Ontario , and more than half of the copper used in the US came from mines along the proposed roadway . Control of the area could have been established by seizing the Soo Locks at Sault Ste . Marie , severing communication lines through the Great Lakes . If the locks fell to an enemy force , no troops or supplies could be moved to the Copper Country except by land . The road was also needed during the five or six months of the year that transportation on the Great Lakes was barred by ice or stormy weather . 
