Britain declared war on Germany on August 4, 1914, after the army of Kaiser Willhelm invaded Belgium.
War had been looming ever since the assassination of the heir to the throne of the Austro-Hungarian Empire Archduke Ferdinand six weeks earlier.
A complicated system of marriage and diplomatic alliances effectively split Europe into two with Austria-Hungary and Italy lining up alongside Germany and France, Britain and Russia opposing the expansionist ideas of the Kaiser.
The British government, which had earlier vowed to protect Belgium, felt that the idea of German troops massing on the other side of the Channel was a step too far.
Within days of war being declared, regular troops – known as the British Expeditionary Force –sailed for France tasked with halting the German advance with many soldiers telling their loved ones they would be home by Christmas.
The first major engagements were the Battle of Mons in August and Battle of the Marne in September and the British and French forces initially had some success.
But as both sides began to dig creating extensive trench systems reaching across North France from the coast to the Swiss border the war in-effect began to stall – trench warfare had arrived.
In October the Belgium border town of Ypres was at the centre of the fighting with the first battle for the control of this strategically important position.
Elsewhere Japan declared its support for the Allies and the Ottoman Empire aligning with the Germans – a true world war was underway.
As well as the fighting on land, the two sides were competing for superiority on the seas. The Kaiser had spent heavily on creating a new modern fleet to challenge Britain’s traditional dominance.
With the battle for Flanders effectively at a stalemate the British government had to take steps to prepare for a drawn-out conflict, a conflict for which in reality it was woefully underprepared.
In March, an extension to the Defence of the Realm Act was passed by Parliament which gave the government extensive emergency powers including control over the press and the workplace.
A coalition government was formed in May and 1915 was the year when women began to take on jobs which previously had been regarded as man’s work.
On the Western Front, the stalemate continued. The second Battle of Ypres saw mustard gas used for the first time.
Bulgaria joined the war on the side of Austria-Hungary and Italy swapped sides to join the Allies.
In April Allied forces began an attack on a new front at Gallipoli in Turkey – an ill-fated campaign which ended in January 1916 with Allied forces, including Australian troops suffering massive losses for no real gains.
The British Navy blockaded German ports and in response, the German began submarine attacks.
In May the passenger liner Lusitania was sunk off the coast of Ireland with the loss of over 1,200 passengers including over 100 Americans.
The year was also notable for the first appearances over London of the dreaded zeppelins which bombed the city – an act which brought the horrors of war to the home front. During the war over 2,000 civilians were killed or injured in air raids.
Conscripition was introduced for men aged 18-41 in February. Around the country, Pals battalions were formed with work colleagues, men from the same town, even from the same football team enlisting together.
In the same month, the German army launched a major offensive on the town of Verdun. The Allies in turn planned a major counter attack along the river Somme.
On July 1 after days of shelling the German lines, the order was given to British troops to advance. Having sat out the aerial bombardment in underground bunkers, the German army was largely unaffected and met the Allied advance with a hail of machine gun fire.
By the end of the day around 60,000 were killed or lay injured on the battlefield making it the blackest day of the war. For the men of the 11th Battalion East Lancashire Regiment 720 ‘went over the top’ at 7.20am. By 8am, 585 were dead, wounded or missing.
As the fighting on the Somme continued, tanks were seen on the battlefield for the first time.
In May, one of the most important battles at sea took place at Jutland which allowed the British fleet to gain effective control of the shipping lanes.
On the home front the move for Irish independence led to the Easter rising when for a short time an Irish Republic was declared before the rebels were defeated by British troops.
The first few months saw major developments in global terms. In Russia, Tsar Nichalas II abdicated after the first of a revolution in February and the October Revolution saw the Bolsheviks led by Lenin assuming total control. This in turn led to an armistice being declared in December 1917, freeing up German troops from the Eastern front.
This was also the year that the Americans declared war on Germany after the German tried to get Mexico to invade the United States. American joining the Allies meant more men, ships and supplies heading to the Western front.
On the battlefield the Germans began the year by retreating to a series of fortified positions known as the Hindenburgh line.
Major battles at Arras and Passchendaele saw casualties continue to rise for little or no gain.
German U-boats were proving hugely effective, hitting goods supplies and leading to the introduction of rationing in Britain. The Atlantic convoys which saw supply boats guarded by warships were also introduced and anti-submarine patrols were stepped up.
In spite of the massive casualties and apparent stalemate on the front line, anti-German feeling remained. Such was the depth of it that King George V made a royal proclamation on July 17 changing the name of the royal family to Windsor from the German Saxe-Coburg.
With the extra resources from the Eastern front at their disposal, German commanders launched a major spring offensive and for three months tried unsuccessfully to break through the Allied forces.
The Allies struck back, first at the Marne and then at Amiens and by autumn the Germans found themselves being pushed back behind the Hindenburg line, short of supplies and facing the prospect of defeat.
At 11am on November 11 an armistice was signed between the Allies and the Germans and the guns fell silent. In four years the Allies lost around six million soldiers, the Germans four million and the total number of military and civilian casualties was over 37 million.
On the home front, the coalition government was re-elected in December, a General Election notable for women over 30 being able to vote for the first time.
Although an armistice had been signed in November, war was not officially ended until June 28, 1919, with the signing of the Treaty of Versailles.