How Does The Civil War Qualify as the First Modern War?

For 5,800 years of recorded history, wars were fought with pre-modern forms of transportation ad communication, where the world was powered by windmills, watermills, literal horse power and human muscle. However, this all changed with the invention of the steam engine and its implementation in the 19th century. In fifty short years, macadamized roads, canals, steam trains, steam boats, steam presses and telegraph communication revolutionized the transfer of energy and power. By the 1850s, every aspect of western civilization looked and functioned differently than it had for thousands of years. It was in this milieu the Civil War was fought. What did the first modern war look like and how did it differ from previous wars? How did wartime observations by foreign emissaries alter the course of future wars?