HELEN SIMPSON
When still a young artillery officer Napoleon Bonaparte married Josephine Beauharnais , who was unable to bear him children. Childlessness mattered little to the young general, but enormously to the Emperor, the would-be founder of a dynasty. For the sake of an heir Napoleon divorced Josephine and married an Austrian archduchess, gaining a faithless ally who turned against him in his hour of need and a son too young to act as his father's deputy when such a deputy might have saved the dynasty.
If the young artillery officer had married a different woman in the first place, the history of Europe might have been altered.