How did WW1 Start? | Causes of the First World War

By the summer of 1914, Europe was in a crisis.  Just weeks before Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, had been  assassinated in Sarajevo by a Serbian-backed terrorist. Now just a few weeks later, the  continent's largest armies were mobilizing against each other with new nations joining the  fight seemingly every week.

The world watched with bated breath as Europe marched to war. So  what happened? How did a seemingly irrelevant local conflict in southeast Europe become a World  War?

And why did Britain decide to get involved? Well before we answer those questions  a reminder to subscribe to the Imperial War Museums Youtube channel for more  videos just like this every two weeks. When people ask how the First World War began it's often couched in terms of a domino effect,  a series of events that were almost preordained, but what I would say is that if anyone  had suggested in June 1914 in Britain that World War might be about to break out  and they would be met with disbelief really.

Britain hadn't fought a war on the continent  since the final defeat of Napoleon at Waterloo, 99 years previously. Rather than a war in Europe, Britain was primarily occupied  with its own internal affairs. As the 20th century dawned Britain is  one of the greatest powers on earth, it rules over this vast global empire. 

I mean it's so big that every fourth person on earth owes its  allegiance to the British crown. The Briton was the world's merchant sailor, his flag encircled the globe sixty percent  of the vessels on any ocean were his. The lifeblood of the British Empire was the sea.

The Royal Navy policed the waves so that its  merchant ships could trade across the globe. This brought the British Empire vast wealth, but  not all of its citizens were able to share in it. Many overseas subjects were demanding  greater freedom from the empire to control their own affairs, while at home  domestic issues threatened to boil over.

There's this huge inequality of wealth that  underpins British life at the turn of the 20th century. Only two-thirds of men have got  the right to vote, absolutely no woman has the right to vote. So I'd say by the time you  get to 1914 this is quite a volatile country.

The most divisive issue, however,  was that of Home Rule for Ireland. Some people in Ireland wanted to be ruled from  Dublin rather than Westminster, while others were bitterly opposed to this, including some vocal  British politicians and a sizable contingent in the north of Ireland who considered themselves  to be British. As the Home Rule Bill made its way through parliament, rival militias began  to arm themselves on either side of the issue.

There is a very real threat that this is going  to spill over into violence in the summer of 1914 and so to suggest to people in Britain that  the conflict that's about to occur will come from Europe rather than from Ireland most people  would have been very very shocked to hear that. But while domestic tensions were rising in  Britain, new tensions were coming to the fore in Europe. Germany was the new kid on the  block with big ambitions.

After defeating France in the Franco-Prussian war of 1870, the most  powerful German state Prussia allied with smaller Germanic states to create a united Germany, but  this new nation wanted an empire of its own. Britain really initially admired this new nation,  Britain really actually thought as a friend but imperial Germany soon began to  threaten Britain's sense of supremacy. Its determination to up its industrial output, up its military strength, and most crucially  for Britain build a rival fleet of warships.

German ships manoeuvre in the  cold waters of the north sea. This new German navy was a threat  to Britain's naval dominance, the glue that held the empire together, and  something for which Britain could not stand. That rivalry then turned into an arms race  as each nation tried to outproduce the other with ever greater feats of technology. 

This culminated in the production of Dradnought battleships which were seen  as the nuclear weapons of their day. That factor means Britain's now  started to see Germany as a threat, by the time you get to say 1907 Europe's  really split into two opposing camps. Germany had disturbed the delicate  balance of power in Europe.

France, fearing this new empire on their doorstep, allied  with Russia in the east. An unlikely friendship for two of Europe's most ideologically opposed  nations. That then left Germany feeling surrounded and pushed them to form an alliance with  the Austro-Hungarian Empire and to a lesser extent Italy.

Finally, Britain and its empire,  afraid of German domination on the continent, drifted closer to France and Russia, though  without going as far as forming an alliance. You've got Germany Austria-Hungary and  Italy and you've got France Russia and to some extent Britain. There's still no  immediate reason for war between the two, it would take a crisis to turn  tensions into an armed conflict.

And that crisis came in the summer of  1914. The Balkans in Southeast Europe had been a hotbed of unrest for some time,  with two wars in the preceding three years. Those wars had made Austria-Hungary's neighbour  Serbia much larger, prompting tensions between the two nations to rise even further.

When Archduke  Franz Ferdinand was assassinated in June by a Serbian-backed terrorist, Austria-Hungary felt  it had no choice but to assert its dominance. Austria-Hungary sets out to punish Serbia it  wants to quash support for Serbian nationalism. It's encouraged by its ally Germany.

So  after Serbia failed to meet the terms of a very draconian ultimatum Austria-Hungary  declares war on Serbia and this act of war this stirs up these old tensions and anxieties right across the continent because it draws  in supporters and allies on both sides. When Austria-Hungary declared war on Serbia Russia  came in to back the Serbs in defence of a fellow Slavic nation. When Germany, in support of its  ally, then declared war on Russia that brought France into the war on Russia's side.

Italy  however did not join the war, as its alliance with Germany and Austria-Hungary was a defensive  pact. In a matter of weeks then Europe's largest powers were primed for war, but Britain was still  in two minds over whether it should be involved. It agonized over whether to support  Russia and France.

I think at the heart of Britain's anxieties it came down really to  Britain fearing German domination of Europe because if a victorious but hostile  Germany dominated the continent and threatened Britain's position in the world  that was just intolerable for Britain. The tipping point came thanks  to Germany's war plans. Hoping to defeat France quickly before  Russia had a chance to mobilize her forces, Germany attempted to skirt around the  French defences in Alsace-Lorraine by attacking through neutral Belgium,  a country Britain had sworn to protect.

On the 4th of August Britain issues an ultimatum  to Germany which is ignored, which ends in Britain declaring war on Germany and by Britain declaring  war on Germany that also means its global empire is at war and you have a conflict set  up that becomes very rapidly a world war. The causes of the First World War are complex,  they're still debated to this day. The nations didn't realize it at the time, but their attempts  to defend what they perceived as their own national interests created a war that would shape  Europe for decades to come.

Most participants expected the war to be over by Christmas, but  as we know the reality was very different. The First World War became  what we would call a total war. These nations pitted against each other, millions  of men fighting on land, on the sea, in the air, modern weaponry causing mass casualties and  ultimately the war broke the empires of Germany, of Russia, Austria-Hungary, it forced the USA onto  the world stage and the war also laid the seeds for future conflict in places like the Middle  East.

So it ultimately defined the shape of Europe and the world in the 20th century  and this is how it all began.