World War 1: Causes, Fronts and Consequences, Explained Simply

One assassination, and five weeks later Europe is at war

On 28 June 1914, in Sarajevo, a Serbian patriotic organisation killed Archduke Franz Ferdinand, heir to the Austro-Hungarian throne. Anyone who reads that date as “the cause” of World War 1 stops too early: a full month separates the assassination from the first declaration of war, and everything is decided in that month.

Austria-Hungary, backed by Germany, sent Serbia an ultimatum on 23 July. On 28 July it declared war. From there the sequence ran fast: Germany declared war on Russia on 1 August and on France on 3 August, and between 1 and 4 August it violated the neutrality of Luxembourg and Belgium. That violation is what brought Britain into the conflict. Japan joined on 23 August; the Ottoman Empire sided with the Central Powers on 12 November 1914.

The real cause lies deeper: a system of alliances in which each power was bound to follow its ally, inside an imperial rivalry built up over the preceding years. Serbia, having gained territory from the Ottoman Empire and sure of Russian backing, had its eye on the Habsburg provinces; Austria intended neither to make territorial concessions nor to tolerate Russian interference. On that ground, a political murder was enough to set the whole mechanism going.

The line that stopped moving

The German plan had been drawn up in 1905 by General von Schlieffen and later entrusted to von Moltke. It called for a quick victory in the west: break through via Belgium and Luxembourg and knock France out in a few weeks.

On the ground it stopped. The Battle of the Marne, from 5 to 10 September 1914, reversed the course of events, and the operations that followed fixed the front along a trench line cutting across the continent from the Belgian coast to neutral Switzerland. That line is the image that best sums up the whole war in the west: through three years of attrition it moved only a few kilometres, back and forth, at an enormous cost in lives.

Behind that stillness lies a technical reason. The spread of automatic weapons made the defender far stronger than the attacker, and attacking in the open cost losses out of all proportion to the ground gained. This was the shift from a war of movement to a war of position, or attrition, and World War 1 is the textbook case.

Practical example: Verdun, which began on 21 February 1916, and the Somme, from 1 July to 23 November of the same year, are two battles that lasted months, fought over a front that had barely moved since 1914. They were not exceptional episodes. They were the ordinary way that war was fought.

Societies at war had to reorganise completely. Around 65 million men were mobilised in all, and national economies were converted to war production, from factories to transport. It is a conflict in which what we now measure as GDP, the value of what a country produces in a year, becomes a weapon in its own right.

The Italian front: from the Isonzo to the Piave

Italy was tied to Germany and Austria-Hungary by the Triple Alliance, but stayed out in 1914. It renounced the alliance on 3 May 1915, having signed the Treaty of London with the Entente on 26 April, and declared war on Austria on 24 May.

The main front was the Isonzo, where General Luigi Cadorna launched four offensives in 1915 alone, between 23 June and 5 December. In August 1916 the sixth battle took Gorizia; in the eleventh, between 17 August and 15 September 1917, the advance reached ten kilometres. Eleven offensives for ten kilometres: that was the ratio of effort to result on that front.

On 24 October 1917 an Austro-German attack broke the Italian lines at Caporetto. The retreat halted on the river Piave, where command passed to Armando Diaz. In the Battle of the Piave, from 15 to 19 June 1918, the Italians lost 90,000 men and the Austrians 150,000. The final offensive set out on 24 October 1918: Vittorio Veneto was taken on the 29th, and the troops went on to reach Trento and Trieste.

1917 changes the balance

Two opposite events fall in the same year, and between them they settle the war.

On one side, the United States. The sinkings of the British liners Lusitania and Arabic had cost the lives of 131 American citizens; after the steamer Sussex was torpedoed in March 1916, Germany accepted the so-called Sussex pledge on 4 May. On 31 January 1917 it announced the resumption of unrestricted submarine warfare. Meanwhile, on 19 January, the British had intercepted the telegram in which Arthur Zimmermann, the German Foreign Secretary, proposed that Mexico make war and peace together with Germany, with generous financial support and the prospect of reconquering the lost territory of Texas, New Mexico and Arizona. They passed it to President Wilson on 24 February, and on 1 March the story became public. Wilson requested a declaration of war on 2 April: the Senate voted in favour on 4 April, the House on 6 April 1917. On 7 December the United States also declared war on Austria-Hungary.

On the other side, Russia, overwhelmed by revolution, left the conflict: an armistice on 15 December 1917, the Treaty of Brest-Litovsk on 3 March 1918. The Central Powers freed up troops in the east, but too late to offset the arrival of American resources.

The collapse came in the autumn, one armistice after another: Bulgaria on 29 September 1918, the Ottoman Empire on 30 October, Austria-Hungary with Italy on 3 November, Germany on 11 November.

What it cost

This is where the sources disagree most, so a caveat first. Treccani gives roughly 8 million dead and 20 million wounded. The International Encyclopedia of the First World War, which rebuilt the counts nation by nation, arrives instead at 10,057,600 military deaths: 5,647,600 among the Allies and 4,410,000 among the Central Powers.

Country	Military deaths
Germany	2,037,000
Russian Empire	1,997,500
Austria-Hungary	1,513,500
France and colonies	1,400,000
Britain and Empire	959,000
Ottoman Empire	772,000
Italy	600,000
United States	87,900

Those same authors warn that the figures remain problematic: definitions of a war death vary from one country to the next, wounded men evacuated and later returned to duty were sometimes counted more than once, and some national statistics carry political bias. Estimates of civilian deaths diverge even more widely, from a few tens of thousands to several million depending on the method.

A peace that left questions open

The peace conference opened in January 1919 at Versailles, just outside Paris, with nearly thirty nations, but the decisions were taken by the “Big Four”: Britain, France, the United States and Italy. The Treaty of Versailles, signed on 28 June 1919, dealt with Germany alone, which gave up about 10 per cent of its prewar European territory and all of its overseas possessions; Danzig and the Saarland passed under League of Nations administration. Article 231 assigned it responsibility for the conflict and the liability to pay reparations, later set at 132 billion gold marks, equal to 32 billion US dollars at the time, on top of an initial payment of 5 billion dollars.

Those reparations were denominated in gold marks, not in paper currency. A debt denominated in paper money can be eroded by inflation, that is, by the currency losing purchasing power; tying it to gold was meant precisely to prevent that. Which is why the real weight of those sums could not be lightened by printing banknotes. And for any debtor, the headline amount is not the whole story: what it costs to refinance the debt matters too, and that depends on interest rates.

The other defeated empires required separate treaties: Saint-Germain with Austria (10 September 1919), Neuilly with Bulgaria (27 November 1919), Trianon with Hungary (4 June 1920), Sèvres with Turkey (10 August 1920). Out of the dissolution of the empires came Poland, Czechoslovakia, Yugoslavia, Finland, Lithuania, Latvia, Estonia and Albania, while many borders were redrawn.

One detail explains a good deal of what followed: the United States never ratified Versailles. The Senate objected above all to Article 10 of the League of Nations covenant, arguing that it handed an international body the power to commit the country to war; the vote of 19 March 1920 fell seven short of ratification. Washington later signed a separate peace with Germany, the Treaty of Berlin, on 25 August 1921. The League of Nations, founded in 1919 to build a new system of international relations, proved largely ineffective.

Politically, the outcome is clear-cut: Europe came out weakened, the United States rose on the world stage — only to withdraw again after the isolationist victory of 1920 — and 1919 saw the founding of the Communist International. Europe emerged from the conflict with fewer men, less capital and less productive capacity: the conditions under which economic activity contracts, what we now call a recession. Many questions, though, were simply postponed: Italy obtained its Alpine border but no settlement of the Adriatic question with the new Yugoslav state, and none of the colonial compensation it had expected. Twenty years later, many of those questions were still unresolved.