WW1: Why did Britain join the First World War?

It is more than 106 years since Britain’s entry into the First World War, one of the bloodiest conflicts in history.

Tensions had been brewing throughout Europe for years, particularly in the Balkan region of the southeast, before World War I actually broke out.

A number of alliances involving European states, the Ottoman Empire, Russia and other parties had existed for years, but political instability in Bosnia and Serbia threatened to destroy those agreements.

Amid these rising tensions, with hindsight the world seemed poised for conflict, but the scale of that conflict and its impact would become larger than any that had ever come before it.

World War One would involve 32 nations across its four years, with empires falling and new states being born.

More than 1.1 million people would die serving the British Empire.

The Spark Which Ignited War

While the reasons for the Great War were varied and complex, one event has been argued to be the decisive trigger that began it all.

On 28 June 1914 the Archduke Franz Ferdinand, heir to Austria-Hungary’s throne, was assassinated by Serbian nationalist Gavrilo Princip.

Princip and other nationalists in his group, the Black Hand, were attempting to end the rule of Austria-Hungary over Bosnia Herzegovina.

What followed for the next 37 days became known as the July Crisis, a diplomatic frenzy which saw events across Europe escalate quickly.

The assassination was blamed by Austria-Hungary, like many countries around the world, on the Serbian Government and it was hoping to use it as a justification to settle the question of Serbian nationalism.

Russia’s support for Serbia, meant that Austria-Hungary waited to declare war until they were sure they had the support of Germany.

Without the support of German leader Kaiser Wilhelm II Austria’s leaders feared that a Russian intervention would involve Russia’s ally, France, and potentially Great Britain as well.

On 5 July, Kaiser Wilhelm gave the country a "blank check" assurance of German backing in any coming war.

With that reassurance Austria-Hungary provided Serbia with an ultimatum with terms so harsh acceptance was all but impossible.

Under increasing pressure and fearing war, the Serbian government mobilised its army and appealed to Russia for assistance. 

Austria-Hungary would declare war on Serbia on 28 July, with World War One following soon after.

What Brought Britain Into The War?

Germany soon declared war on France, military allies of Russia since 1894, and on 3 August employed the Schlieffen Plan.

It was an aggressive military plan designed to bolster Germany's chances in the face of a war on two fronts, Russia in the East and France in the West.

Named for its mastermind Alfred von Schlieffen, it required the German army to invade France via Belgium, ignoring the Treaty of London that had guaranteed Belgian neutrality since 1839.

Germany anticipated little resistance from Belgium and referred to the treaty as simply 'a scrap of paper'.

As one of the treaty’s signatories Britain issued Germany an ultimatum to retreat from Belgium by midnight on 3 August 1914 or Britain would declare war in defence of Belgium’s neutrality.

With no response given late on 4 August 1914, Britain declared war with Germany and officially entered the war on the side of the Allies.

The idea that neutrality might not be respected, that powers would simply ignore it, was something that alarmed the British.

Breaking that fundamental principle led to a worry that it may set a troubling precedent for other countries, in part because the UK had often been neutral themselves.

This coupled with the prospect of the whole of the opposite seacoast being controlled by a hostile power, as well as crucial waterways that led into Europe, was more than enough motivation.

Key Moments Involving Britain During World War One

• 28 June 1914: Archduke Franz Ferdinand is assassinated.
• 28 July 1914: Austria-Hungary declares war on Serbia, beginning First World War.
• 2-7 August 1914: Germany invades Luxembourg and Belgium. France invades Alsace. British forces arrive in France.
• 10 August 1914: Austria-Hungary invades Russia.
• 9 September 1914: Allied forces halt German advance into France during First Battle of the Marne.
• 18 February 1915: Germany begins naval blockade of Great Britain.
• 25 April 1915: Allied forces land on the Gallipoli Peninsula of the Ottoman Empire.
• 23 May 1915: Italy declares war on Austria-Hungary.
• 21 February 1916: Germany begins the attack on Verdun.
• 31 May 1916: Naval Battle of Jutland takes place between British and German fleets.
• 1 July 1916: Allied offensive begins the Battle of the Somme.

• 18 December 1916: Battle of Verdun ends with 550,000 French and 450,000 German casualties.
• 3 February 1917: United States severs diplomatic relations with Germany.
• 6 April 1917: The United States declares war on Germany.
• 24 June 1917: American combat forces arrive in France.
• 15 December 1917: Russia signs armistice with Germany.
• 3 March 1918: Russia signs the Treaty of Brest-Litovsk with Germany.
• 21 March 1918: Germany begins its final offensive of the war.
• 2 June 1918: American forces stop German attempt to cross the Marne River at Chateau-Thierry.
• 26 September 1918: Allied forces begin the attack at Meusse-Argonne, the final offensive of the war.
• 11 November 1918: Germany signs the Armistice at Compiègne, ending World War One.
• 1 December 1918: British and American forces enter Germany.
• 14 February 1919: Draft of the covenant of the League of Nations is completed.
• 28 June 1919: Allied and German representatives sign the Treaty of Versailles. 
• 10 January 1920: Treaty of Versailles takes effect.

The Human Cost Of The War

World War One lasted about four years and its human cost was immense.

Its casualties dwarfed all conflicts that came before it. Some 8,500,000 soldiers died as a result of wounds and/or disease, according to statistics from Britannica.

The increased mechanisation of the war meant that even on quiet days on the Western Front hundreds of soldiers on both sides would die.

The heaviest loss on a single day happened on 1 July 1916, during the Battle of the Somme, when the British Army suffered 57,470 casualties.

Statistics from the Britannica show the number of casualties for the Allied and Associated Powers:

• Russia - 1,700,000
• British Empire - 908,371
• France - 1,357,800
• Italy - 650,000
• United States - 116,516
• Japan - 300
• Romania - 335,706
• Serbia - 45,000
• Belgium - 13,716
• Greece - 5,000
• Portugal - 7,222
• Montenegro - 3,000

The Central Powers also suffered big losses:

• Germany - 1,773,700
• Austria-Hungary - 1,200,000
• Turkey - 325,000
• Bulgaria - 87,500

Cover image: World War One British soldiers in a trench at the Western Front in France (Picture: PA).