War of the Third Coalition

By 1805, Britain had convinced Austria and Russia to join a Third Coalition against France. Napoleon knew the French fleet could not defeat the Royal Navy in a head-to-head battle and planned to lure it away from the English Channel. The French Navy would escape from the British blockades of Toulon and Brest and threaten to attack the West Indies, thus drawing off the British defence of the Western Approaches, in the hope a Franco-Spanish fleet could take control of the channel long enough for French armies to cross from Boulogne and invade England. However, after defeat at the naval Battle of Cape Finisterre in July 1805 and Admiral Villeneuve's retreat to Cadiz, invasion was never again a realistic option for Napoleon.
Instead, he ordered the army stationed at Boulogne, his Grande Armée, to march to Germany secretly in a turning movement—the Ulm Campaign. This encircled the Austrian forces about to attack France and severed their lines of communication. On 20 October 1805, the French captured 30,000 prisoners at Ulm, though the next day Britain's victory at the Battle of Trafalgar meant the Royal Navy gained control of the seas. Six weeks later, on the first anniversary of his coronation, Napoleon defeated Austria and Russia at Austerlitz. This ended the Third Coalition, and he commissioned the Arc de Triomphe to commemorate the victory. Austria had to concede territory; the Peace of Pressburg led to the dissolution of the Holy Roman Empire and creation of the Confederation of the Rhine with Napoleon named as its Protector.
Napoleon would go on to say, "The battle of Austerlitz is the finest of all I have fought." Frank McLynn suggests Napoleon was so successful at Austerlitz he lost touch with reality, and what used to be French foreign policy became a "personal Napoleonic one". Vincent Cronin disagrees, stating Napoleon was not overly ambitious for himself, that "he embodied the ambitions of thirty million Frenchmen".