The creation of a unified Italy and Germany altered the balance of power in Europe in the 1860s and 1870s. Nationalism, imperialism, great-power alliances, and public opinion—influenced by newspapers and photos—helped fuel tensions. By the early 1900s the Triple Alliance and the Triple Entente had taken shape. A naval arms race between Germany and Britain as well as diplomatic and military crises in Morocco, the Balkans, and elsewhere contributed to an uneasy peace.

The peace conference first met formally on January 18, 1919. Nearly thirty nations involved in the war against the Central Powers sent delegates. Russia was not represented. The defeated nations took no part in the deliberations; the Germans, in particular, were given little chance to comment on or criticize the terms offered them. German anger over this failure of the Allies to accept their new republic was to play a large part in the ultimate rise of Adolf Hitler.

The most worrisome crises were in Russia. No sooner had the Germans been forced to withdraw from the regions they had gained at Brest-Litovsk than the Allies sent detachments to various points along the perimeter of Russia—on the Black Sea, on the White Sea in the far north, and on the Pacific. The Allies’ dread of final Bolshevik success and of the possible spread of Bolshevism westward added to the tensions at Versailles.

The warring powers met at Versailles to settle with the Germans and at other châteaux around Paris to settle with the rest. Peace congresses never meet in a world that is really at peace, for there is always an aftermath of local war, crises, and disturbances.

In 1918-1919 these were so numerous and acute that they conditioned the work of the peace congresses. In addition, throughout 1918-1919 an influenza epidemic more devastating than any disease since the Black Death swept across the world, taking 20 million lives and disrupting families and work everywhere.

In World War I soldiers and sailors were, for the most part, civilians, unused to military ways. Behind the front—subject to rationing and regimentation in daily living—families, too, were part of this great “total war.”

They, too, bore up under it, though in France in 1917, after the bloody failure of the “one big push,” civilian and military discontent almost broke French morale. And in Germany the armistice was the result, in part, of a psychological collapse under intolerable spiritual and material pressures.

Both sides knew that the entry of the United States, with its fresh forces and vast industrial capacity, would be telling, were the war to last another year. But the Central Powers anticipated victory before American forces could be in the field.

This war also saw the beginnings of air warfare. German dirigibles (known as Zeppelins) raided London many times in 1916 and 1917, and both sides made airplane bombing raids on nearby towns. But the total damage was relatively light and did not affect the final result. The airplane was more important for scouting. The fighter plane was greatly improved during the war, and a base was laid for the development of the modern air force.

In the long run British sea power and American supplies proved decisive. The Allied command of the sea made it possible to draw on the resources of the rest of the world, and in particular to transfer large numbers of British and later American troops to the crucial western front.

This truly worldwide war, fought in the Near East, Africa, and the Far East, as well as in every ocean, made it clear that non-Continental events were no longer mere sideshows. The war in the Near East, in particular, would unleash nationalisms that continue to the present day.

Ultimately more significant was the Dardanelles campaign of 1915. With the entry of Turkey into the war on the side of the Central Powers in November 1914, and with the French able to hold the western front against the Germans, a group of British leaders decided that British strength should be put into amphibious operations in the Aegean area, where a strong drive could knock Turkey out of the war by the capture of Constantinople.

In the meantime, in April 1915 Italy had concluded with Britain, France, and Russia the secret Treaty of London, which promised the Italians Trent and Trieste plus other lands at Austro-Hungarian and Turkish expense. In May the Italians formally declared war on Austria-Hungary, and a new front was added along the Austro-Italian frontier at the head of the Adriatic.

The eastern front, where the Russians faced both the Germans and the Austrians, was crucial to Allied tenacity in the West. Millions of men were involved on both sides, and had the Russians not held out until the end of 1917, the Allies in the West could hardly have withstood the reinforcements that the Germans and Austrians would have been able to send to France and Italy. Though the war in the East was more fluid than the war in the West, even in the East there were long periods of stalemate.

The German attack through Belgium was the first stage in the plan prepared by Alfred Graf von Schlieffen (1833-1913), chief of the general staff from 1891 to 1906. The strong right wing was to take Paris and fall on the rear of the French, who would be pinned down by the left wing.

With France quickly eliminated, the Germans would then unite their forces and attack the Russians, who would still be in the throes of mobilization. Britain, an island nation, would be held off and attacked if necessary.

Even before the American entry, the Allies had an overwhelming superiority in total population and resources. The Central Powers had in their own Continental lands not more than 150 million people; Britain, France, Russia, and Italy in their own Continental lands had at least 125 million more people than their enemies.

World War I took the lives of 8 million soldiers, and caused far more deaths through malnutrition, war-spawned diseases, and birth deficits arising from economic dislocations and the loss of precisely the age-group most likely to beget children.

The collapse of the Russian economy, followed by widespread famine and epidemic, meant that, despite staggering military losses, northwestern Europe emerged from the war in a dominant position once again.

Why did war begin precisely where and as it did? Need all the nations that were drawn into it have participated? Which nation was primarily responsible for causing the war? Within that nation, which groups, which leaders?

Given war, need it have taken the form that it did? In part because the victor writes the history, the majority of historians have blamed Germany or the tottering Austro-Hungarian Empire for the war. However, most historians do agree on certain matters concerning the outbreak of the war.

By August 6, when Austria declared war on Russia, all the members of the Triple Alliance and the Triple Entente had entered the war, with the exception of Italy, which declared neutrality. The Central Powers of Germany and Austria-Hungary stood against the Allies—Russia, France, Britain, and Serbia.

The diplomats and statesmen were drawn into war because they believed that a diplomatic defeat or loss of face for their nation was worse than war. Austria-Hungary believed that the Serbian government had had some suspicion of Princip’s assassination plot and should have given Austria warning.

After 1871 Bismarck sought to isolate France diplomatically by building a series of alliances from which it was excluded. He sought to keep on good terms with both Austria and Russia, and, what was more difficult, to keep both these powers on good terms with each other. Since both wanted to dominate the Balkans, Bismarck’s task was formidable.

Nationalism and the accompanying shifts in the balance of power both influenced and were profoundly influenced by public opinion, often shaped by the public press.

Throughout western Europe and in the United States a jingoistic press, often intent on increasing circulation, competed for “news,” and not all papers were careful to separate the verifiable from the rumor, the emotional atrocity story (even when true) from the background account that would explain the context for the emotion.

One factor that made war more likely was the unification of Germany and of Italy. The creation of these two new major states altered the balance of power in the European state system; the efforts of statesmen during the next forty years to adjust the system ultimately proved unsuccessful.

The older established powers were unwilling to give up their own claims, and after 1850, with the principle of national sovereignty well established, smaller western European states were no longer open to annexation by the great powers.

In June 28, 1914, the Habsburg arch duke Francis Ferdinand, heir to the throne of Austria-Hungary, and his wife, Sophie Chotek, were assassinated in the streets of Sarajevo, capital of the province of Bosnia, which had been occupied by Austria-Hungary since 1878.

The assassin, Gavrilo Princip (1895-1918), was a Serbian nationalist. The Austro-Hungarian government, alarmed by the ambitions of Serbian nationalists, took the occasion of the assassination to issue a severe ultimatum to Serbia.