There have been a great many books written about the Battle of the Marne in September 1914, so why you ask do we need one more? Professor Holger H Herwig's narrative of the battle seeks to diverge from the standard Anglo-French historiography of the battle and look at it from the German perspective (i.e. more on how the battle was lost, rather than how it was won). His primary hypothesis about the root cause of the German defeat is that faulty command and control (C2) techniques - including poor leadership in key positions - doomed the so-called Schlieffen Plan. It is a good hypothesis which the professor does an effective job of supporting, although he does not mention that there are competing hypotheses, such as Martin van Creveld's well-argued Supplying War (1977), which shows that the Schlieffen Plan was logistically unsound. Other hypotheses argue that von Moltke, the Chief of the German General Staff, doomed the Schlieffen Plan by excessive operational changes. Herwig also provides value-added content by incorporating documents gleaned from recently-released archives in former East Germany, although this represents only a tiny portion of his supporting evidence. Overall, the strength of Herwig's The Marne 1914 is as a fine analysis of command and control failure at the operational-level.
Unfortunately, there are a number of irksome qualities about this book, beginning with the awful maps copied from the West Point Atlas of WW1. It is extremely difficult to follow unit movements or actions on these maps (e.g. von Gronau's impressive spoiling attack on the Ourq River that robbed Joffre's counterstroke of surprise and Third Army's night bayonet attack that threw Foch's Ninth Army back (the map shows only some arrows, but no indication where the corps and divisions the author mentions were located). While there are some first-person accounts incorporated, overall the author's battle narrative is rather sterile and difficult to follow. He also put me off at the beginning when he stated that the "Battle of the Marne" was not just about the actions fought on the outskirts of Paris, but about the entire campaign fought between 1 August and 10 September 1914. His early chapters on the frontier battles seem to distract from his main hypothesis and then once the action heats up around Paris he simply drops coverage of Alsace-Lorraine. Finally, the author never really gets into the nuts and bolts of military doctrine, tactics or organization. When he claims that each German corps had 144 135-mm guns (in fact, the German Army had a total of only 4 13.5cm K09 guns in 1914), which would translate into over 4,000 13.5cm guns, it's easy to see that he has skimmed over important details. Instead, the author spends a great deal of time discussing German atrocities committed against civilians in Belgium - which again is not very germane to his hypothesis.
Professor Herwig is on firmer ground with the faulty C2 hypothesis. He points out that unlike the elder von Moltke in the successful 1870-71 France-Prussian War, the younger Moltke made no effort to get out of his headquarters in Luxembourg and spent the entire campaign hundreds of miles from the front. This "chateau generalship" could have been mitigated if Moltke had used telephones and couriers to keep in touch with his advancing armies, but Herwig does a good job pointing out how little the German army made use of the latest means of communication in 1914. Not only did Moltke not have reliable communications with each army, but the armies could barely communicate with their neighbors on each flank or with their subordinate corps. Finally, once the Allies began their counterattack on the Marne, the weakness of key commanders such as von Bulow aggravated the inability of Moltke to orchestrate the campaign. Some of this more a question of leadership rather than C2 per se. Overall, this a very well-argued hypothesis, but whether or not it was THE key reason why the German invasion failed is less certain. Van Creveld's hypothesis also demonstrated that the Germans simply could not effectively supply their armies outside Paris, while the French were fighting right next to their main supply base. Herwig also comments that the French commander, Joffre, relied on interior lines and railroads to shift troops to the Paris area to gain a numerical superiority at the critical point, while Moltke was relying on exterior lines and infantry marching on foot; this seems like a no-brainer at any military staff college, but apparently it never occurred to von Schlieffen or Moltke. In short, why were the Germans surprised that the French could quickly transfer troops to defend their capital? Another related reason for the German defeat that the author brings up, is that the Germans were surprised that the French still had the spirit to launch furious counterattacks after weeks of retreating - this suggests that the General Staff based too much of their planning on the enemy they fought in 1870, not the one they would face in 1914.
In the end, the author essentially concludes that the great German General Staff and a few key commanders suffered a mental melt-down on 6 September 1914 and robbed Imperial Germany of possible victory. He does not claim that German victory was inevitable if they had not retreated from Paris, but he does suggest that they might have at least walked away with some tactical victories on the Ourq and against Foch's 9th Army that could have left them in a better position for the fall campaigns. Perhaps.