Nineteen forty is one of the key dates in French history, like 1789 or 1871, when sensational events gripped the country and the world. Rebecca West said that the fall of France was "a tragedy that ranks as supreme in history as Hamlet and Othello and King Lear rank in art". Historians have always been puzzled about this debacle. When the armistice with Germany was signed on 22 June 1940, the Nazi war machine had defeated one of the most powerful nations in Europe in just six weeks, in a textbook demonstration of blitzkrieg.
The battle for France was not one of the Second World War's bloodiest - insignificant alongside Stalingrad - but between 50,000 and 90,000 Frenchmen died and a million and a half were taken prisoner (as against German losses of 27,074 dead and 111,034 wounded). Apart from seeming to lay Britain open to imminent invasion, the fall of France created a power vacuum that would lead to genuine world war in 1941, when Italy and Japan moved in to take advantage of stricken Marianne, and Hitler was able to turn on the Soviet Union earlier than expected. French history, too, changed utterly because of 1940, because without that national disgrace the conditions would not have been propitious for the later rise of Charles de Gaulle to supreme power.
How does one explain the debacle? In an extremely lucid and absorbing account, Julian Jackson works carefully through the possible answers. He begins by stating his belief (and here he is correct) that there really are single years in history that change everything. He examines the parochial French view that 1940 was all the fault of the perfidious British, but finds this is a non-starter. Franco-British relations were always fraught but the French must bear the major blame: they failed to co-ordinate their military operations properly with their allies and had already, through their disastrous foreign policy in the 1930s, gained a reputation for duplicity and unreliability.
Jackson asks whether the collapse in 1940 might not ultimately have been a moral problem, when a corrupt and decaying Third Republic cracked under the strain. He establishes that France was close to civil war in 1936, when Leon Blum's Popular Front took office, and identifies a running antagonism between the military and the government that was healed only in the early 1960s under de Gaulle. In the end, he discounts factors of morale and of social and economic weakness as being ultimately significant. In truth, the France of 1914 was more brittle than that of 1940, yet she survived. And even 1940 in England, now encrusted with the barnacles of Churchillian legend and swathed in the nimbus of the "finest hour", could easily have turned out very differently - as Jackson shows in a stimulating, counterfactual essay.
Jackson's final answer to the conundrum of 1940 is unfashionable but probably correct: it was a contingent military defeat where the Germans employed the element of surprise and were rewarded by staggeringly good luck. Above all, he condemns the lacklustre French intelligence services.
As is well known, in the 1930s the French relied heavily for defence on the Maginot Line. They did not, as is often foolishly thought, fail to foresee that the Germans would evade the line by attacking through Belgium: invading through Belgium was precisely what they wanted Germany to do, as it allowed their army to be concentrated there in depth. This strategy was torpedoed in 1936, when Belgium announced its neutrality. But the French still remained confident, sure that the Wehrmacht would have to advance through northern or central Belgium; they thought the barrier of the River Meuse made a German thrust through southern Belgium impracticable. Nor were they significantly inferior in technology to the German military. It is often said that the French were prepared only to fight the First World War again, but this is an oversimplification. They were abreast of all the new strategic ideas but did nothing to implement them in daily practice and, above all, they failed to relate the work of their intelligence agencies to operational planning.
The Germans, on the other hand, took a heavy gamble. An offensive through the Ardennes would leave their armies dangerously exposed at the most critical juncture, and the Meuse loomed as a forbidding barrier. Aided by copious and well-composed maps, Jackson shows that the so-called "Manstein plan" was an ingenious variant of the 1914 Schlieffen plan whereby, instead of cutting off the allied armies by swinging south-east (the 1914 idea), the Wehrmacht would achieve the same result by swinging north-west after emerging from the Ardennes. The plan was audacious, almost too much so; Hitler came close to cancelling it on several occasions because he saw that it might end in a German military catastrophe. Perhaps this was the point where the feuding between Generals Weygand and Petain, on the one hand, and the prime minister Paul Reynaud, on the other, really made its mark. But for Jackson, in the main, French culture, society and politics explain the consequences of the fall of France, rather than its causes.
As with 1940 in England, there will be more to say on this fateful year from various viewpoints, but any future synthesis will have to take account of Jackson's superb reconstruction, which melds expert military knowledge with riveting mini-biographies of the principal players. This is history as it should be written.