In 1804, Napoleon Bonaparte ordered the kidnapping of the Duc D'Enghien, an insignificant aristocrat who was based in Baden, beyond France's borders.

Napoleon had somehow decided that this deluded and ineffectual nobody, who lived on a British pension, represented some kind of danger to him. D'Enghien was duly executed, to the despair of some of Napoleon's erstwhile supporters, notably the great writer Chateaubriand, who up till then had given the Corsican the benefit of the doubt, and had been a reluctant supporter.

D'Enghien's capture and killing were brutal and unnecessary, for he was hardly a threat to Napoleon. But by now Napoleon wielded supreme, total power and was ready to exterminate his enemies, real or imaginary. He was getting out of control. Yet his career had been notable up till then for almost inhuman control and the most rigorous self discipline.

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Napoleon, born in relative obscurity in Ajaccio, Corsica, had made superb use of his training at a provincial military academy and then at the elite ecole militaire. He emerged as a military leader of undoubted and possibly unparalleled genius. He was also a brilliant politician; he seized on the confusion and near anarchy that followed the French Revolution in 1789. With consummate cunning he manipulated bureaucracies and orchestrated claques. He picked his self-serving way through the chaotic residue of the revolution with cold, careful precision.

Indeed, he relished the political and social uncertainty that characterised France in the decade following the Revolution, for these provided him with opportunities he would not otherwise have had. He created some kind of order out of chaos and propelled himself to the forefront of France and, indeed, Europe. Only Britain stood in the way of total domination.

The paradox was that while he was a supreme opportunist and risk taker, for the most part he maintained iron personal discipline. He was essentially an adventurer, but as a personality he was somewhat buttoned up. He was perhaps history's ultimate careerist, and rigorous personal mastery, particularly in his early years, underpinned his success.

His remarkable rise was predicated on his emergence as a military commander who could provide victory after victory, often against the odds. An outsider who was rapidly promoted above older and more experienced officers, his promotions were justified.

His troops, for the most part, adored him. He could communicate with them as a brother, and he showed unusual concern for their welfare as well as leading them with inventive dash and tactical gusto. He almost, but not quite, became the master of Europe.

This was because his mastery on land deserted him on water. He never learned how to deploy naval power. Despite having been born and brought up in a coastal town on an island, he failed to understand the sea. This is the one great mystery about him. He may have cut swathes across mainland Europe, but he could never grasp the nature of sea power. Just one commander inflicted not one but two grievous and momentous defeats on him. Significantly, this was an admiral, Lord Nelson.

Had Britain not been an island, it is probable that Napoleon would have conquered it. As it was, he never got the measure of Britain, and Britain never understood him. Even now there is a split in British attitudes to him. Some regard him as Europe's ultimate hero; others see him as a blood-soaked megalomaniac who was almost as bad as Hitler. The truth lies, of course, somewhere in the middle.

This new biography by the Oxford historian Michael Broers is judicious, but it only takes us up to 1805, when Napoleon was just 36 years old and still had much to achieve, and also much to destroy. The second and concluding part of the massive biography must be eagerly awaited, for it will surely attempt a concluding audit of the life, a considered judgment on the whirlwind and its residue.

As he guides us through the almost unbelievably action-packed first 35 years, Broers is sure-footed and sympathetic, but never guilty of adulation. He is good at placing Napoleon in his complex context; a time of violent, constant upheaval - much of which was caused by Napoleon himself. He writes well, and of the very many books on Napoleon, this will without doubt become regarded as one the best. But for all that, I suspect only an out-and-out military man could really understand Napoleon. The key to him is that he was the ultimate soldier.

Michael Broers will be discussing his biography of Napoleon at Aye Write! on April 5,