1900

As of March 1 (O.S. February 17), when the Julian calendar acknowledged a leap day and the Gregorian calendar did not, the Julian calendar fell one day further behind, bringing the difference to 13 days until February 28 (O.S. February 15), 2100. The year 1900 also marked the Year of the Rat on the Chinese calendar. January 1900 January 2 – U.S. Secretary of State John Hay announces the Open Door Policy, to promote American trade with China. January 3 – The United States Census estimates the country's population to be about 70 million people. January 5 – Henry A. Rowland of Johns Hopkins University announces a theory about the cause of the Earth's magnetism. January 6 – Second Boer War: Boers attempt to end the Siege of Ladysmith, which leads to the Battle of Platrand. January 9 - Italian club SS Lazio is founded in Rome. January 9 - The first through passenger train goes from Cairo to Khartoum. January 14 Puccini's opera Tosca premieres in Rome, Italy. The U.S. Senate accepts the British-German Treaty of 1899, in which the United Kingdom renounces its claims to the American Samoa portion of the Samoan Islands. January 24 – Second Boer War – Battle of Spion Kop: Boer troops defeat the British Army. January 27 – Boxer Rebellion: Foreign diplomats in Peking, Qing Dynasty China, demand that the Boxer rebels be disciplined. January 31 – Datu Muhammad Salleh, leader of the Mat Salleh Rebellion in North Borneo, is shot dead in Tambunan. February 1900 February 5 – The United Kingdom and the United States sign a treaty for the building of a Central American shipping canal across Central America in Nicaragua. February 6 – The International Arbitration Court at The Hague is created, when the Netherlands' Senate ratifies an 1899 peace conference decree. February 8 – Second Boer War: British troops defeat the Boers at Ladysmith, South Africa. February 14 – Second Boer War: Battle of Paardeberg – 20,000 British troops invade the Orange Free State. February 15 – Second Boer War: The Siege of Kimberley is lifted.