1800

1800 was a year in the early 19th century marked by continuing political realignments and scientific advances. In Europe, the French Republic under the Directory continued the wars of the Revolutionary era, and Napoleon Bonaparte cemented his position with a decisive victory at Marengo in June. In the same year, France and Spain signed the secret Treaty of San Ildefonso, in which Louisiana was ceded to France to be delivered in 1803.

In the United States, the presidential election of 1800 culminated in a tie between Thomas Jefferson and Aaron Burr in the Electoral College. The contest was resolved by the House of Representatives, which elected Jefferson as president, marking a peaceful transfer of power between rival political factions. The United States also conducted its second census in 1800, recording a growing population and westward expansion.

In the British Isles, the Act of Union 1800 united the kingdoms of Great Britain and Ireland into the United Kingdom of Great Britain and Ireland, taking effect January 1, 1801. In science, Italian physicist Alessandro Volta demonstrated the voltaic pile, the first practical source of continuous electric current, a milestone in electrochemistry and electrical engineering.