Generally I see nothing against people stepping outside their own area of expertise; such forays can lead to new insights and fresh ideas but only if they are carried out with a certain amount of humility and respect for the knowledge of those who are specialists in the area. Unfortunately this is not Professor Mosier's way; his approach is arrogant and he holds military historians in contempt - the first lines of the Preface to the Paperback Edition reveal that he has an enormous chip on his shoulder (perhaps as a child he was frightened by a historian).
He also holds the British and French military leaders of the First World War in contempt. Maybe he is right to do so but this is hardly new. It is rather difficult to know what 'myth' Mosier thinks he is busting.
The book is well written (as you would hope from a Professor of English) but there is a certain amount of avoidable repetition and the narrative is marred by minor errors and omissions; for instance, the reader is informed that some event occurred 'on the 23rd' but then has to hunt around to work out which month is being referred to. Mosier is also sometimes lax over compass points, so Meaux, for instance, is described as north of Paris rather than east. The maps that accompany the text are inaccurate sketches that do not help, curious for an author who is, quite rightly, concerned with details of terrain, strategic points and lines of communication. There are some other curiosities. Mosier's comments on the aerial war are strange. I do not believe that aerial bombardment was more accurate in the First World War than in later periods and I have never read such a claim before. He also seems to assume that the Germans had aerial superiority over the Western Front throughout the War, which is incorrect; certainly they had it at times, such as during the Second Battle of Arras which coincided with 'Bloody April' 1917, but not at other times.
Mosier's maths are also suspect. On page 148 he says that the French General Staff's estimates of numbers of troops on both sides of the lines, 14 Allied men for every 11 Germans, were 'wildly inaccurate'. He then gives some precise figures showing that the French had about 2.1 million men on the Western Front and the Germans about 2.2 million in early 1915. He then makes the rather vague statement that the Belgians and British 'together hardly came to another half a million'. This can only mean, presumably, that there were (just) half a million Belgian and British troops. I am no mathematician myself but that means that there were 13 Allied men for every 11 Germans, so the French estimates were hardly 'wildly' inaccurate. In a sense this is an unimportant point because Mosier goes on to argue, rather more convincingly, that firepower mattered far more than manpower in the First World War, but it make me suspicious of his other claims. Another aspect of this is his statement that most casualties in the War were caused by artillery, whereas in earlier wars small arms had been more destructive. This is partly true but it doesn't take into account the calculation that between a quarter and a third of all military deaths in the First World War were due to disease. Nowhere in his extensive use of casualty figures does Mosier acknowledge this.
Mosier is full of praise for German strategy and tactics, pointing out that the successes of the German army in the Second World War owed much to the tactical developments of the First. This is certainly true but again it is not a new idea. I remember reading this in Len Deighton's book 'Blitzkrieg' years ago. Ultimately Mosier's thesis is that the Allies had lost the War by early 1918 and that only the intervention of large numbers of American troops turned the tide and defeated the Germans. Whether this rather simplistic analysis is correct I am not sure but I don't think any serious historians have ever much doubted the considerable impact of fresh American forces in the final stage of the War. It is curious again that Mosier bases his analysis of Allied defeat largely on casualty figures, despite his well-made argument that it was firepower, not men, that mattered.
At the end of the book Mosier writes with misplaced pride of the hubristic American War memorials that disfigure the French countryside and contrasts them with what he sees as the neglected French cemeteries. He is of course full of praise for the well maintained German cemeteries but interestingly he does not mention the Commonwealth War Graves Commission; their cemeteries are every bit as well designed and maintained as the German ones but if he is unable to criticise a British institution he ignores it.