Sir John Keegan’s admirably concise history of the second greatest war of the 19th century begins “America is different”. This difference, all the more pronounced 150 years ago, is key to understanding the social, political and, above all, military aspects and outcomes of a war whose long shadows still lie across the American landscape.

Some of the differences at first appear trivial: the civil war was the worst tailored of any great conflict, Keegan says. This reveals both the problem of rapid expansion of the armies and the general militia-mindedness of the troops, who were not as amenable to the military discipline visited on conscripts and volunteers across the Atlantic. But they were better fed armies than any before them, the result of abundant agriculture, manufacturing processes and efficient distribution. Keegan’s observations on the human and logistic factors are fascinating and, if at times sweeping, still contain the essence of what made the war different. Keegan’s lifelong study of war and engagement with American history from his earliest years endow his prose with a majesty of judgment that younger bucks might tilt at.

The civil war began with the famous shots fired at Fort Sumter in 1861, lasted until after the assassination of President Lincoln in 1865 and was fought to determine whether the United States could indeed survive united. That determination cost more than 600,000 military deaths, more than any war in which Americans have fought. The principal reason was strategic, Keegan argues: the nature of the Confederacy and the size and geography of the country presented Washington with “one of the most complex military problems ever to face war-making governments”. Not only had President Lincoln (and Jefferson Davis in the South) and his advisers to raise a great army, they had to determine how to use it to gain victory.

For the South it was perhaps easier: it had “only” to avoid being defeated, whereas the North had to overcome the Confederacy, which meant defeating its armies, to take possession of the country. Yet the South’s lack of unity of effort would not help its cause; and the inferiority in manpower, stores and lack of a navy did not seem to hold out much chance of success. Little surprise, then, that the Confederacy put great faith in “King Cotton” to lever support from those European nations — Britain, in particular — whose cotton manufacturing industry depended on Southern exports. And so the war became one of the most ferocious yet fought, for without real strategic objects for the armies to manoeuvre against, what could they do but fight each other in battle after battle?

The British Army paid the war little heed. The nation’s military eye was on its imperial needs; continental warfare, requiring a larger army than the country possessed or was willing to pay for, was to be avoided. And what could this “affair of militias”, as it was dismissed, teach about continental war with great standing armies such as those of France and Prussia? And what lessons in generalship from a corps of trained officers only 3,000 strong?

Yet, as Keegan says, it is remarkable that from this small number America produced “two unquestionably great soldiers, Grant and Sherman, of whom Sherman was also a visionary”. After the Second World War British officers studied the civil war: in the 1950s and 1960s it was part of the syllabus for the Staff College entrance exam, and the young Keegan taught it to Sandhurst cadets. It has fallen out of fashion once more. This is a pity, for to ponder such intractable politico-military problems cannot but be useful. For a start to such study, it is hard to see how Keegan’s masterful and thought-provoking book could be beaten.

The American Civil War by John Keegan (Hutchinson, £25; Buy this book; 416pp)

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