Few moments in the history of Europe rival 1812 for drama. Emperor Napoleon turned on his erstwhile Russian ally, launching in June an invasion force of 500,000 soldiers. It captured Moscow in October. The Grande Armée was compelled to retreat before the year was out, however. Strangled logistics, frigid weather, and resistance by Czar Alexander's troops routed a seemingly invincible military machine led by a genius. The tattered remnants of the Grande Armée were then abandoned in December by Napoleon. He hastened home to a somber Paris. The sweep of Alexander's victory was abundantly clear to America's envoy in St. Petersburg, John Quincy Adams. He recorded in his diary in early December: “Within the compass of ten days the Russian armies have taken between forty and fifty thousand prisoners, with cannons, baggage, and ammunition in proportion. There is nothing like it in [saga] since the days of Xerxes.”

British–Spanish–Portuguese armies supervised by Sir Arthur Wellesley (later Duke of Wellington) meantime continued to fight French forces in the Iberian peninsula. They had entered in 1808. They were not expelled until 1813. Francisco de Goya etched the unforgiving Peninsular War that featured atrocities against civilians plus guerrilla tactics. His series, The Disasters of War, stood unmatched for more than a century as pictorial depiction of war's grotesqueness – until another Spaniard, Pablo Picasso, painted Guernica.

Military operations in 1812, stretching from Russia to Spain, culminated in French defeat at Leipzig, October 1813. Napoleon abdicated in April 1814.