On this day: 31 May

A Mongol army under Genghis Khan captured Zhongdu (modern Beijing), the capital of the Jin dynasty of China.

Mongol invasion of Kievan Rus': Mongol forces defeated a Kievan Rus' army at the Battle of the Kalka River in present-day Ukraine.

Majapahit forces under Raden Wijaya won a major victory in the Mongol invasion of Java, now considered to be the founding date of the Indonesian city of Surabaya.

Cardinal Bessarion announced his donation of 746 Greek and Latin codices to the Republic of Venice, forming the Biblioteca Marciana.

The United States enacts its first copyright statute, the Copyright Act of 1790.

Manuel Quimper explores the Strait of Juan de Fuca.

Qajar Iran and the Ottoman Empire determine their international boundary in the second treaty of Erzurum.

American Civil War: Confederate troops under Joseph E. Johnston and G. W. Smith engaged Union forces under George B. McClellan at the Battle of Seven Pines outside Richmond, Virginia.

American Civil War: Overland Campaign: Battle of Cold Harbor: The Army of Northern Virginia engages the Army of the Potomac.

Gilmore's Garden in New York City is renamed Madison Square Garden by William Henry Vanderbilt and is opened to the public at 26th Street and Madison Avenue.

The Second Boer War came to an end with the signing of the Treaty of Vereeniging in Pretoria, South Africa.

The National Negro Committee, forerunner to the National Association for the Advancement of Colored People (NAACP), convenes for the first time.

The South Africa Act comes into force, establishing the Union of South Africa.

The President of Mexico Porfirio Díaz flees the country during the Mexican Revolution.

World War II: Imperial Japanese Navy midget submarines begin a series of attacks on Sydney, Australia.

Ferenc Nagy, the democratically elected Prime Minister of Hungary, resigns from office after blackmail from the Hungarian Communist Party accusing him of being part of a plot against the state. This grants the Communists effective control of the Hungarian government.

The Uniform Code of Military Justice takes effect as the legal system of the United States Armed Forces.

The U.S. Supreme Court expands on its Brown v. Board of Education decision by ordering district courts and school districts to enforce educational desegregation "at all deliberate speed."

The South African Constitution of 1961 becomes effective, thus creating the Republic of South Africa, which remains outside the Commonwealth of Nations until 1 June 1994, when South Africa is returned to Commonwealth membership.

In Moscow City Court, the Rokotov–Faibishenko show trial begins, despite the Khrushchev Thaw to reverse Stalinist elements in Soviet society.

In accordance with the Uniform Monday Holiday Act passed by the U.S. Congress in 1968, observation of Memorial Day occurs on the last Monday in May for the first time, rather than on the traditional Memorial Day of May 30.

The Trans-Alaska Pipeline System is completed.

The Ariane 2 rocket is launched on its maiden flight, carrying Intelsat VA F-14, but the mission ends in failure.

Bicesse Accords in Angola lay out a transition to multi-party democracy under the supervision of the United Nations' UNAVEM II peacekeeping mission.

Air France retires its fleet of Concorde aircraft.

Vanity Fair reveals that Mark Felt was "Deep Throat".

Usain Bolt breaks the world record in the 100m sprint, with a wind-legal (+1.7 m/s) 9.72 seconds.

Space Shuttle Discovery launches on STS-124 carrying the second portion of the Japanese Kibō module to the International Space Station.

The asteroid 1998 QE2 and its moon make their closest approach to Earth for the next two centuries.

Syrian civil war: The Syrian Democratic Forces (SDF) launch the Manbij offensive, in order to capture the city of Manbij from the Islamic State of Iraq and the Levant (ISIL).