The best case I can make for one person altering the course of history is Joan of Arc. She arrived on the scene fourteen years after the Battle of Agincourt. England had won legal title to the throne of France. It controlled the cathedral at Rheims where all French kings were crowned. It even ruled Paris. French forces had suffered fourteen years of uninterrupted defeats. Orleans, their last city north of the Loire, was about to capitulate under siege. That river formed the only natural boundary defending the bulk of their remaining lands. French loyalists were openly questioning whether their country could continue to exist.
It was precisely because the situation seemed so hopeless that the nobility paid moderate attention to a religious peasant girl. Nothing else was working. Would-be mystics were commonplace. This one might help morale.
What no one expected was that she would lead the most successful campaign of the hundred years’ war, crown the dauphinking of France, and secure the country’s future.
They gave her a suit of armor and put her on parade, then excluded her from serious meetings. She burst in anyway. They went into battle without waking her up. She rode onto the field anyway. Armies were small enough then that a single combatant might inspire victory or defeat. During the final battle for Orleans she sustained a wound that would define her reputation. A crossbow bolt sank six inches into her shoulder. She pulled it out with her own hands and went back to lead the next charge.
Two centuries earlier Richard the Lion Hearted had done the same thing. He died of infection three weeks afterward. Three weeks after Joan of Arc’s wound she was clearing English outposts from the Loire valley and climbing a scaling ladder when a stone cannonball split in two against her helmet and knocked her to the ground. She survived that too and marched on Rheims the next month.
French captains who fought alongside her testified the highest respect for her military skills, especially artillery arrangements, and agreed that she was the driving force behind France’s aggressive advances during the summer of 1429. The next spring she was captured when she insisted on being last to leave the field during a retreat. A French courtier named la Tremoille tried to promote a boy shepherd to take her place as peasant visionary. The English drowned him in the Seine.
French advances continued at a sluggish pace after her death. By then their task was easier: the lands she had reconquered significantly increased the tax base, several key English leaders had died or been captured, and the battle of Patay had essentially dismantled the English army.