Barbara Tuchman, The Guns of August (1963)

Highly recommended.
The second Tuchman book I have read. This by legend is the one Jack Kennedy read and it scared him when he thought about nuclear weapons.
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One of Tuchman’s major themes is that a plan carefully made in detail and extensively supported takes on a life’s of its own.  If a small shove engages the plan, then it takes a super-human effort to divert it, stop it.  (When President Kennedy abruptly gets up from the table and walks out of the room while the Air Force generals are arguing for bombing Cuba in the film ‘Thirteen Days’ that is one example of the effort to resist a plan in the face of enormous pressure.) In 1914 the Germans had the most extensive and detailed plan for war of all time and so were the most bound by it.  It specified the train cars platoons would ride it and at what place and time they would, dismount from Mobilization Day (or M40) plus 40 in Paris. Once the plan was initiated everyone knew what to do and set about doing it. Belgian resistance which had been set at 0 in the plan broke down the schedule and traffic jams resulted. The perfect plan contained an erroneous assumption. But that dislocation simply made it more imperative to get back on schedule, not to think twice about the plan. The General Staff set to work around the clock to re-route trains, to re-supply units, to to find alternative roads, to shift rolling stock, and so on.
Another general theme is the difficulty of getting anyone to obey orders. French, German, Russian, and English generals refused orders, stalled, deliberately misunderstood, or willfully rendered themselves incommunicado.  Even when the superior officer came and delivered the order face-to-face in person the response was sometimes tomorrow, not just yet, or no. At times it was impossible to replace this general so he stayed in command and did not move. The Prussian General Francois waited and stalled and stalled until he was ready to move on his terms. The Prussian Von Kluck ignored his order and improvised in the hope of a magnificent coup and blundered.
In the same vein, she stresses the general confusion of war. The German Chief of Staff had little idea of what the situation with his own armies was, let alone where the French or English were and in what force.  Ditto for corps and division commanders.  
Another theme is the logistic of moving regiments, divisions, corps, and armies. The staff work was crucial. To move 70,000 armed men with artillery and other equipment takes a very great deal of detail and direction, a timetable for movement, an allocation of roads or railroad cars, fodder and food along the way, and much more. It all makes Sydney’s Town Hall Station at peak hour seem organized.
The tangled web of secret treaties, each with its conditions and conditionals, made it difficult for anyone to predict what would happen.  And even where there was a simple and clear treaty inevitably it was made by someone else a few years ago and the question of the will of the current incumbents to live up to it arose.
The disobedience gave scope for individuals to make a difference.  Her study by the way is all at the command level, generals and up, not grunts. 
Of personalities, the Kaisar seems a loose cannon who wanted to show the world Germany was a great power. The French general Joffre made many mistakes, none of which he ever admitted, but was a rock of calm and optimism.  French, the English commander, lost his nerve not even a personal visit from Kitchner could stiffen him. 
The contradictory character of orders plays into the disobedience.  A general is ordered to attack but cautioned not to expose his flank.  A general is ordered to be aggressive but not to risk defeat.  Which part takes priority, aggression or risk avoidance?
Galiani seems to have been the man for the hour at the Marne.  His idea of a long meeting was 15 minutes, all else was action.  He was a general without an army for the most of the time but that only slowed him down, it did not stop him.  The taxi cabs were but one of his initiatives.
King Albert of Belgium was ready to fight from the first and did not relent when the Germans started shooting civilian hostages. Even a German effort to buy him off for an enormous sum was rejected.
The Russians fulfilled their French alliance by attacking long before they were ready and that led to be a major defeat from which they never recovered, but it did draw off two German army corps from the invasion of Frances and that helped weaken the German advance in the West. There are many ifs and might have beens. 
Even the most bellicose commanders, when the order to attack came, hesitated, trimmed, temporized.
She has many masterful turns of the phrase. Impressive research and synthesis from original sources.  The scope is everything that happened in August 1914, well literally from the July assassination to the started of the Battle of the Marne in mid-September.  
The tactical of manuals of the Russian army placed little emphasis on shells for either rifles or cannons, but instead stressed sabres and bayonets. The German manual told attackers to run 20 seconds then fall down while the enemy fired every 20 seconds. After they have fired get up and run again.  But the fire rate was 8 seconds as it turned out.
Though most of the weapons, artillery and machine guns, that dominated World War I were used by the Japanese against the Russia in Asia, and dutifully reported by the European military attachés who observed the Russo-Japanese War, virtually nothing of that made its way into the manuals, the ministers of war, or generals.
Personal rivalries and antagonisms between generals often spoiled plans.
The capacity of politicians to dither in the hope that the crisis would dissipate of its own accord in England and France is worth reading.  Even with the Germans 40 miles from Paris no democratically elected office holder would permit General Galini to demolish building to create firing lines.  Instead they argued over who would pay compensation to the owners and questioned the necessity of destroying bridges to impede the German advance.  Galini wanted to mine all the bridges over the Seine and delegations of historians opposed him. There was very little singular focus even with the Barbarians at the gates.
Speaking of barbarism, the German atrocities in Belgium did occur and they were systematic.