"He Walked Around the Horses" is a science fiction short story by H. Beam Piper. It is initially based on the true story of diplomat Benjamin Bathurst, who mysteriously disappeared in 1809. It was first published in the April 1948 issue of Astounding Science Fiction magazine (now Analog). The story is told in epistolary style, as a series of reports, statements and memoranda by various government, army and police officials, and inn servants, stating what they know of the matter.
Benjamin Bathurst, a British diplomat, disappears whilst staying at an inn in Prussia. Piper describes Bathurst in the story as "a rather stout gentleman, of past middle age". However, the real Bathurst was born in 1784, and thus 25 years old at the time of his disappearance.
This story posits that Bathurst slipped into a parallel universe. The point of divergence from our history is the Battle of Quebec (1775) in which Benedict Arnold is killed (instead of merely wounded), leading to the 1777 victory of British General John Burgoyne over American General Horatio Gates at the Battle of Saratoga. Consequently the American Revolution and French Revolution both fail, and there were no Napoleonic Wars. The alternate Bathurst served as the Royal Governor of Georgia, still a British colony. Napoleon Bonaparte is a colonel in the French Army and Talleyrand has remained in ecclesiastical orders and risen to become Cardinal. George Washington was killed in battle at Doylestown during the short-lived rebellion of the colonies in British North America. Moreover, Thomas Jefferson - the author of the American rebels' Declaration of Philadelphia - fled to Havana, eventually dying in the Principality of Liechtenstein, while James Madison is in exile in Switzerland. The Bathurst from our timeline is judged to be either insane, or a spy, and imprisoned. He attempts to escape and is fatally shot.
Bathurst's diplomatic documents are read by a high ranking British officer. He is amused by Talleyrand's role as Bonaparte's advisor and eminence grise, a role he finds plausible. But he is especially puzzled by references to a British general named "Wellington". In the final line of the story, the British officer is revealed to be Sir Arthur Wellesley (who in our time is better known as the Duke of Wellington).
Robert Sobel's 1973 novel, For Want of a Nail, has the same point of divergence from our history, but mostly follows the alternative history of America, instead of the impact on Europe.