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EXPLAINER: The First World War
Photo: Photo: Irish Life, 21 August. Full collection of Irish Life is available in the National Library of Ireland.

EXPLAINER: The First World War

Why did the First World War break out?

The immediate cause of the war was the assassination by Bosnian Serb conspirators of the heir to the Austro-Hungarian throne, Archduke Franz Ferdinand, on 28 June 1914. The ensuing diplomatic crisis is known as the July crisis. By late July, Austria-Hungary had declared war on Serbia, while on 1 August, Germany declared war against Russia and two days later against France. On 4 August, Britain declared war on Germany, so that five of the European great powers and two ‘small states’, Serbia and Belgium, were now at war.

The scene as Gavrilo Princip approached the car in which the Archduke and his wife were travelling and fired the shots that would prove fatal for both of his targets. (Image: Das Interessante Blatt, 2 July 1914, ANNO/Austrian National Library)

In the years before the July crisis, there had been major crises and chronic tensions in European politics. The Balkan Wars in 1912 and 1913, the arms races on land and at sea, and the formation of two alliance blocs both caused and reflected the fraying of the bonds of peace. That said, by early 1914, many observers considered that European states had safely negotiated some of the most dangerous international crises and that the revived Concert of Europe, used to great effect in late 1912 and early 1913, signalled a more stable future. The course of the July crisis dashed these hopes and therefore must be considered a key cause of  the war, not a mere trigger.

Where was the war fought?

The war expanded rapidly. While the major land battles were fought on the western and eastern fronts, the war had already begun to assume its global character in the autumn of 1914. The Japanese seizure of German colonies in China and the fighting in East and West Africa showed how the expansion of European empires in the late 19th century embroiled large areas of the globe in what was initially a conflict between European states. In late 1914 and early 1915, the Atlantic became an important battleground, as the Allies sought to blockade the Central Powers, Germany and Austria-Hungary, and Germany responded with submarine campaigns.

Photo: © 2000 by Cartography Associates

The war also expanded due to the entry of states into the conflict. The decision of the Ottoman empire to join the Central Powers in November 1914 meant that Anatolia and  Mesopotamia became major theatres of war. The entry of Italy (May 1915) and Romania (August 1916) on the side of the Allies and of Bulgaria (September 1915) on the side of the Central Powers further expanded the war. The American decision to enter the war in 1917 was partly due to the German decision to re-open unstricted submarine warfare (suspended after American protests in 1915) and the (largely fantastical) prospect of a German alliance with Mexico.

Each theatre had important regional consequences, but the war was won and lost on the western front. Paradoxically the greatest changes came in other regions, especially with the emergence of new states in central and eastern Europe and the Middle East.

How was the war fought?

From Gallipoli to the Marne, from the eastern front to the Alps, trenches became the dominant feature of battlefields in the First World War. Soldiers initially dug trenches as a response to withering firepower. By early 1915, this tactical response became a central strategic and operational problem, particularly on the western front. Here there was less space compared to the eastern front, there was a higher density of troops, and railway infrastructure enabled armies to move troops rapidly towards areas where the enemy threatened a breakthrough.

Engineering a breakthrough preoccupied the leading generals on both sides, though some such as Eric von Falkenhayn, chief of the German General Staff between 1914 and 1916, and Ferdinand Foch, who became the generalissimmo of the Allies in 1918, argued for a form of attritional warfare that would break the manpower resources and morale of the enemy – ‘bleed the enemy white’, to use Falkenhayn’s pithy and brutal description of the operational logic that lay behind the battle of Verdun.

The King's Liverpool Regiment at Givenchy suffered heavily while trying to penetrate the Germans' wire entanglements. (Image: Illustrated London News [London, England], 27 March 1915)

As the trench systems developed, artillery became the dominant weapon. Artillery was responsible for the vast majority of deaths on the western, eastern, and Italian fronts. Some studies have suggested that soldiers in general found artillery bombardments even more terrifying than ‘going over the top’.

There were moments when movement was restored to the battlefield, but paradoxically the army which made the most gains, often hollowed itself out, making it vulnerable to counter-offensives and damaging morale. The Brusilov offensive by the Russian army in the summer of 1916 made significant gains at the expense of Austro-Hungarian forces, but the loss of officers and the stretched supply lines contributed to the dissolution of the Russian army in 1917. In spring 1918, using mobile storm troop units supported by coordinated artillery shelling, German forces pushed back Allied forces. Yet the loss of elite troops and extended trenchlines contributed to the successive defeats inflicted by French, British, and American forces in July and August 1918. By that time, the Allies had begun to integrate tanks and airplanes into operations. The Allied counter-offensive from July 1918 forced the German Supreme Command to decide to ask for a ceasefire.

How was the war won and lost?

Historians have offered three broad answers to this question. First the western allies won important military victories against German forces in the summer and autumn of 1918. The German army was on the verge of collapse when the armistice was agreed in November 1918. For much of the war, German forces had adapted more readily to battlefield conditions than their enemies – and their allies for that matter. While proficient in solving the tactical and operational challenges of the battlefield, German generals were unable to reconcile their limited military power to their expansive war aims. By 1917 and 1918 French and British generals had also adapted to battlefield conditions, but with greater manpower and economic resources, the Allies were in a better position to achieve their own very extensive war aims.

The Allies attempt to fight back the German monster. Photo: / Bibliothèque nationale de France

They key to victory and defeat lay in the vast superiority of Allied resources. The Allies had more men, more labour, higher industrial production, and access to greater financial resources. This reflected their larger resource base at the beginning of the war. Britain’s entry tilted the economic balance from the Central Powers to the Allies. Their empires provided food, men, and industrial resources – 1/3 of British shells fired on the western front in 1917 were manufactured in Canada, for example. When Russia dropped out of the war in 1917, the entry of the United States more than compensated. Already the chief creditor to the Allies, the United States industrial capacity dwarfed that of other states. The Allied armies had massive superiority in planes and tanks at the end of the war, facilitating battlefield victories. Crucially the western Allies also had better food supplies. In general this was due to more efficient agricultural techniques, though the Allied naval blockade also contributed to the food crises in Germany and Austria-Hungary. Allied distribution and rationing systems were more effective than those of the Central Powers. While the health of the British civilian population improved over the course of the war, there was an estimated 600,000 excess civilian deaths - a measure of premature death – in Germany over the course of the war.

The relative economic advantages of France, Britain, and the United States also bolstered the legitimacy of their war effort. That these states were also democracies and relied on popular self-mobilization has also been put forward as an explanation for victory against the autocratic regimes of Germany and Austria-Hungary. Russian collapse and revolution was further evidence of the failure of authoritarian states to sustain a popular war effort between 1914 and 1918. However an explanation for victory and defeat that relies on the virtues of constitutional democracies and the limitations of autocratic regimes should not be pressed too far. The governments in France, Britain, and the United States suppressed dissent, often with a heavy hand. Nor is it clear that parliamentary institutions played a greater role in France or Britain than in Germany, for example. One distinct difference was that the Allied politicians exercised more control over the military than their German counterparts, particularly in 1917 and 1918, when Paul von Hindenburg and Eric Ludendorff came to dominate German decision-making to fatal effect.

Dr William Mulligan teaches modern international history at UCD. He is the author of The Creation of the Modern German Army (Berghahn, 2005); The Origins of the First World War (Cambridge, 2010) and The Great War for Peace (Yale, 2014).


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