On this day: 18 September

Constantine the Great decisively defeated Licinius in the Battle of Chrysopolis, establishing Constantine's sole control over the Roman Empire and ending the Tetrarchy.

Byzantine–Seljuk wars: Byzantine forces defeated their Seljuk opponents in the flanks of the nocturnal Battle of Kapetron, but learned of their Georgian allies' defeat in the centre the next morning.

Philip Augustus becomes king of France at the age of fifteen.

Thirteen Years' War: In the Battle of Chojnice, the Polish army is defeated by the Teutonic knights.

The expedition of Juan Bautista Pastene makes landfall in San Pedro Bay, southern Chile, claiming the territory for Spain.

The twelfth baktun in the Mesoamerican Long Count calendar begins.

The Treaty of Belgrade is signed, whereby Austria cedes lands south of the Sava and Danube rivers to the Ottoman Empire.

French and Indian War: The Articles of Capitulation of Quebec are signed.

First Government Junta in Chile. Though supposed to rule only during the Peninsular War in Spain, it is in fact the first step towards independence from Spain, and is commemorated as such.

Tiffany & Co. (first named Tiffany & Young) is founded by Charles Lewis Tiffany and Teddy Young in New York City. The store is called a "stationery and fancy goods emporium".

The United States Congress passed the Fugitive Slave Act, decreeing that all escaped slaves be brought back to their masters.

The New York Times, the largest metropolitan newspaper in the United States, was founded.

Wars of Italian Unification: Battle of Castelfidardo: Royal Sardinian Army defeats forces of the Papal States, resulting in the conquest of Umbria and Marche by the Kingdom of Italy.

The Confederate States celebrate for the first and only time a Thanksgiving Day.

American Civil War: John Bell Hood begins the Franklin–Nashville Campaign in an unsuccessful attempt to draw William Tecumseh Sherman back out of Georgia.

The first provincial election for the Nova Scotia Legislative Assembly after Canada's Confederation returns a large majority for the Anti-Confederation Party, led by William Annand, who becomes Premier.

The fourth and current State Constitution of Maryland is ratified by voters.

Panic of 1873: The American bank Jay Cooke & Company declared bankruptcy, setting off a chain reaction of bank failures.

The Pacific Stock Exchange opens.

In Washington, D.C., George Owen Squier demonstrated the first system to allow multiplexing of telephone transmissions, sending a message between two laboratories of the U.S. Signal Corps.

The Saturday Evening Post publishes the short story "Extricating Young Gussie" by P.G. Wodehouse, featuring the first appearance of Bertie Wooster and his valet Jeeves.

World War I: The Central Powers' defeat at the Battle of Dobro Pole played a role in the Bulgarian withdrawal from the war and led to the subsequent liberation of Vardar Macedonia.

Fritz Pollard becomes the first African American to play professional football for a major team, the Akron Pros.

In the Netherlands, a law granting full voting rights to women is granted royal assent by Queen Wilhelmina.

Rif War: In Ajdir, Spanish Morocco, a secessionist group of Berbers led by Abd el-Krim proclaim the Republic of the Rif, in rebellion against the Sultan of Morocco and the Spanish Army. French and Spanish forces suppress the Republic by May 1926.

The Kingdom of Hungary is admitted to the League of Nations.

The U.S. ends its military occupation of the Dominican Republic, after invading in May 1916 to force the Dominican government to pay its debts to European creditors.

The Columbia Broadcasting System goes on the air.

Juan de la Cierva makes the first Autogyro crossing of the English Channel.

The Soviet Union is admitted to the League of Nations.

World War II: The Polish government of Ignacy Mościcki flees to Romania.

World War II: The Soviet Union introduces conscription for all males between the ages of 16 and 50.

World War II: Operation Market Garden results in the liberation of Eindhoven.

World War II: The Battle of Arracourt begins.

General Douglas MacArthur moves his general headquarters from Manila to Tokyo.

The National Security Act reorganizes the United States government's military and intelligence services.

Margaret Chase Smith of Maine becomes the first woman elected to the United States Senate without completing another senator's term.

Operation Polo is terminated after the Indian Army accepts the surrender of the army of Hyderabad.

Korean War: The Korean People's Army retreated from the Battle of the Pusan Perimeter after six weeks of fighting, marking the farthest that the KPA would advance in the war.

TV Tupi Difusora, the first television station to broadcast in Brazil, begins transmissions on Channel 3 in São Paulo.

Finnish president J. K. Paasikivi becomes the first Western head of state to be awarded the highest honor of the Soviet Union, the Order of Lenin.

Burundi, Jamaica, Rwanda and Trinidad and Tobago are admitted to the United Nations.

The first television adaptation of Charles Addams's "The Addams Family" premieres on ABC Television.

The 8888 Uprising in Myanmar comes to an end.

General Henri Namphy, president of Haiti, is ousted from power in a coup d'état led by General Prosper Avril.

The Magna Charta Universitatum, asserting key principles essential to the free operation of universities, is signed in Bologna by the rectors of 388 institutions of higher learning, to commemorate the 900th anniversary of the University of Bologna.

An attempted coup d'état against Burkina Faso president Blaise Compaoré is uncovered and foiled.

Liechtenstein becomes a member of the United Nations.

The Anti-Personnel Mine Ban Convention is adopted.

First mailing of anthrax letters from Trenton, New Jersey in the 2001 anthrax attacks.

Buddhist monks join anti-government protesters in Myanmar, starting what some call the Saffron Revolution.

The 2011 Sikkim earthquake is felt across northeastern India, Nepal, Bhutan, Bangladesh and southern Tibet.