Cities around the world dimmed their lights and held ceremonies Monday to commemorate the day "the war to end all wars" began 100 years ago. 

Citizens, politicians and monarchs participated in commemorations and religious services Monday to recognize the 100th anniversary of the beginning of World War I. According to The New York Times, ceremonies brought together former enemy nations in Liège and Mons, Belgium to remember the beginning of the Great War, which began Aug. 4, 1914. 

In London, Prime Minister David Cameron had Britons dim the lights in their homes at 10 p.m. Monday to remember the words of Sir Edward Grey, the British foreign secretary who said at the start of World War I, "The lamps are going out all over Europe; we shall not see them lit again in our lifetime."

The war officially began 100 years ago at 10 p.m. Monday with the declaration of war against Germany. 

A single candle was left burning at 10 Downing Street, and a late-night ceremony was held at Westminster Abbey, where political leaders lit one oil lamp at the tomb of the unknown soldier, which was then extinguished at 11 p.m.

"Sixteen million people perished in World War I," Deputy Prime Minister Nick Clegg of Britain said in a statement. He added that it was "a war which still shapes the world as it is today."

Prince William also stated that the conflict in Ukraine is proof that "instability continues to stalk our continent."

World War I broke out 100 years ago after the assassination of Archduke Franz Ferdinand and his wife, Sophie, on June 28, 1914. The killing was the catalyst for the war that engulfed the world in conflict. 

The United States was neutral at the beginning of the war, then formally joined the battle in 1917. An armistice was signed on Nov. 11, 1918, leaving collapsed empires in its wake and necessitating the redrawing of country boundaries. 

Writer H.G. Wells is often credited with calling the war "the war that will end all war," which became the phrase, "the war to end all wars." Yet, at the war's conclusion, it became clear that World War I would not be a remedy to end the wars that frequently beset humankind.

The conflict was also commemorated Sunday when President François Hollande of France and President Joachim Gauck of Germany hugged at a war memorial in eastern France, which was near the area that was contested between the two countries in the first world war. The ceremony commemorated Germany's declaration of war on France on Aug. 3, 1914. German troops then invaded Belgium, which forced England to join the war the day after. 

Hollande and Gauck also joined politicians from Britain, Belgium and other countries Monday for other commemorations in Belgium. While there were no formal ceremonies in Berlin, Gauck attended ceremonies in areas that were once captured by Germany. 

President Vladimir Putin also inaugurated a World War I memorial in Moscow last week. A museum about the war will soon open in St. Petersburg. The commemoration of World War I in Russia is unusual, as the country usually focuses on commemorating those lost in World War II.

The events of World War I set the stage for World War II and even laid the groundwork for some of the crises occurring in the Middle East and Europe in the present day. 

Prime Minister Cameron said there "were important principles at stake" in WWI before the commencement of a commemorative service at Glasgow Cathedral in Scotland. 

He said those principles include the fact that one power should not dominate Europe and that small countries have a right to exist.