Decades: 1750s 1760s 1770s 1780s 1790s - 1800s - 1810s 1820s 1830s 1840s 1850s
Years: 1798 1799 1800 1801 1802 - 1803 - 1804 1805 1806 1807 1808
William Osgoode, Chief Justice of Lower Canada, ruled that slavery was inconsistent with British Law.
January 30 - Monroe and Livingston sail for Paris to discuss, and possibly buy, New Orleans. They end completing the Louisiana Purchase.
February 24 - The Supreme Court of the United States, in Marbury v. Madison, establishes the principle of judicial review.
March 1 - Ohio is admitted as the 17th U.S. state, retroactive from August 7, 1953.
April 30 - Louisiana Purchase made by the United States from France.
May 18 - The United Kingdom declares war on France after France refused to withdraw from Dutch territory.
July 4 - The Louisiana Purchase is announced to the American people.
July 5 - The convention of Artlenburg leads to the French occupation of Hanover (which had been ruled by the British king).
July 26 - The wagonway between Wandsworth and Croydon is opened, being the first public railway line of the world.
September 23 - British troops defeat an Indian army in the Battle of Assaye
November 30 - At the Cabildo building in New Orleans, Spanish representatives Governor Manuel de Salcedo and the Marqués de Casa Calvo, officially transfer Louisiana Territory to French representative Prefect Pierre Clément de Laussat (just 20 days later, France transferred the same land to the United States as the Louisiana Purchase).
Aargau, Graubünden, St. Gallen, Thurgau, the Ticino, Vaud become Swiss cantons.
Year in topic
1803 in literature
February 2 - Albert Sidney Johnston, Confederate general (+ 1862)
February 15 - John Sutter, California pioneer (+ 1880)
May 12 - Justus von Liebig, German chemist
May 24 - Charles Lucien Bonaparte
May 25 - Ralph Waldo Emerson, essayist (+ 1882)
May 25 - Edward George Bulwer-Lytton, novelist and playwright (+ 1873)
June 24 - George James Webb, composer
July 31 - John Ericsson - Swedish inventor and engineer
November 14 - Jacob Abbott, writer
November 29 - Christian Doppler (Doppler effect)
December 11 - Hector Berlioz, French composer
Jacques-Donatien Le Ray -- a "Father of the American Revolution"
April 7 - Toussaint L'Ouverture, a major Haitian revolutionary.
September 27 - Samuel Adams, American patriot
October 18 - Choderlos de Laclos, author (+ 1803)\n