It was to be the war to end all wars, yet just over 20 years after the First World War ended, Europe was being plunged into a second world war.
It was a war some believed would be contained and over within months, but it killed and wounded 37 million people, soldiers and civilians, in a carnage that lasted four years.
The First World War could be said to have crept up on many in Europe, politicians included.
In the months leading up to it, the political preoccupation in Britain was with Ireland and its move to Home Rule and not events in Eastern Europe.
What happened between 1914 and 1918 did not just alter the world as it was then. It shaped the modern world and its legacies live on - the continuing strife in the Middle East being one example.
In this special section of our RTÉ News site, you can learn a great deal more about the events that led to war in 1914 and their subsequent historical consequences and see, watch and listen to fascinating archive material - including the voices of Irish men who endured the trenches and their horrors.
We have brought together experts such as Professor John Horne of TCD, Editor of the Companion to World War I, and Dr Conor Mulvagh of the Centre for War Studies at UCD.
They have contributed, along with colleagues at RTÉ, a truly enlightening insight into the events of 100 years ago.
RTÉ News Editor Donal Byrne
Survivors of the Somme
Lasting between 1 July and 18 November 1916, The Battle of the Somme was to become one of the defining moments of the First World War. Listen to the Doc on One from 1989 here
The Forgotten War? Ireland and World War I
It Says in the Papers, 7 August 1914
Early casualty remembered
It Says in the Papers, 6 August 1914
The lingering hazards of WWI
Donal Byrne reports that even today in both France and Belgium the legacy of the First World War still poses a risk to the health and safety of many people. Those living on or near former battlefields must deal with many problems ranging from unexploded shells to water contamination.
The Irish in WWI
Watch: Bryan Dobson reports that Irish born soldiers serving in the British Army were involved in fighting in Belgium and France from the very beginning. More than 200,000 Irishmen took part in the war and as many as 36,000 paid with their lives
Irish veterans remembered
Many thousands of Irishmen volunteered to join the British Army, some out of economic desperation, many out of a belief that it would advance the cause of Home Rule. Sinéad Hussey has been looking back at the archives and interviews recorded with veterans of World War One before their deaths.
It Says in the Papers, 5 August 1914
The Great War - Europe Remembers
Britain Declares War on Germany
It Says in the Papers, 4 August 1914
It Says in the Papers, 3 August 1914
Interview: President Michael D Higgins
Why did the World go to War?
Memories of World War I veterans recalled
Talking World War I
My Grandfather's War
My Father's War
My Great War
The Forgotten War
Gallery: Death and Destruction
Gallery: The War Machine
Gallery: Trench Warfare
Gallery: Lights Out
Franz Ferdinand, Gavrilo Princip and the shots that led to WWI
On 28 June 1914, an event occurred that changed the course of history: the assassination of the heir-apparent to the throne of Austria-Hungary, Archduke Franz-Ferdinand, and his wife, Countess Sophie Chotek.