Diplomatic rivalries and international crises played key roles in the rush to war, but a complete understanding of the war’s origins requires an account of the “mood of 1914” — the attitudes and convictions of Europeans around 1914.2 Widespread militarism (the popular approval of military institutions and their values) and nationalism encouraged leaders and citizens alike to see international relations as an arena for the testing of national power, with war if necessary.

Germany was especially famous for its powerful and aggressive army, but military institutions played a prominent role in affairs of state and in the lives of ordinary people across Europe. In a period marked by diplomatic tensions, politicians relied on generals and military experts to help shape public policy. All the Great Powers built up their armed forces and designed mobilization plans to rush men and weapons to the field of battle. Universal conscription in Germany, France, Italy, Austria-Hungary, and Russia — only Britain still relied on a volunteer army — exposed hundreds of thousands of young men each year to military culture and discipline.

The continent had not experienced a major conflict since the Franco-Prussian War (1870–1871), so Europeans vastly underestimated the destructive potential of modern weapons. Encouraged by the patriotic national press, many believed that war was glorious, manly, and heroic. If they expected another conflict, they thought it would be over quickly. Leading politicians and intellectuals likewise portrayed war as a test of strength that would lead to national unity and renewal. Such ideas permeated European society. As one German volunteer wrote in his diary as he left for the front in 1914, “I believe that this war is a challenge for our time and for each individual, a test by fire, that we may ripen into manhood, become men able to cope with the coming stupendous years and events.”3

Support for military values was closely linked to a growing sense of popular nationalism, the notion that one’s country was superior to all others. Since the 1850s the spread of the idea that members of an ethnic group should live together in a homogeneous, united national state had provoked all kinds of international conflicts over borders and citizenship rights. Nationalism drove the spiraling arms race and the struggle over colonies. Broad popular commitment to national interests above all else weakened groups that thought in terms of international communities and consequences. Expressions of antiwar sentiment by socialists or women’s groups were seen as a betrayal of country in time of need. Inspired by nationalist beliefs, much of the population was ready for war.

Leading statesmen had practical reasons for promoting militarism and nationalism. Political leaders had long used foreign adventurism and diplomatic posturing to distract the people from domestic conflicts. In Great Britain, leaders faced civil war in Northern Ireland and a vocal and increasingly radical women’s movement. In Russia, defeat in the Russo-Japanese War (1904–1905) and the revolution of 1905 had greatly weakened support for the tsarist regime. In Germany, the victory of the Marxist Social Democratic Party in the parliamentary elections of 1912 led government authorities to worry that the country was falling apart. The French likewise faced difficult labor and budget problems.

Determined to hold onto power and frightened by rising popular movements, ruling classes across Europe were willing to gamble on diplomatic brinksmanship and even war to postpone dealing with intractable social and political conflicts. Victory promised to preserve the privileged positions of elites and rally the masses behind the national cause. The patriotic nationalism bolstered by the outbreak of war did bring unity in the short run, but the wealthy governing classes underestimated the risk of war to themselves. They had forgotten that great wars and great social revolutions very often go hand in hand.