By the time of the Civil War, the railroads had advanced to allow the movement of large numbers of troops even though railways had not yet matured into a truly integrated transportation system. Gaps between lines, incompatible track gauges, and other vexing impediments remained in both the North and South. As John E. Clark explains in this compelling study, the skill with which Union and Confederate war leaders met those problems and utilized the rail system to its fullest potential was an essential ingredient for ultimate victory.