The single most significant background factor to the war was the rivalry that existed between Europe’s “great powers” by the beginning of the twentieth century. The term “great power” meant something specific in this period of history: the great powers were those able to command large armies, to maintain significant economies and industrial bases, and to conquer and hold global empires. Their respective leaders, and many of their regular citizens, were fundamentally suspicious of one another, and the biggest worry of their political leadership was that one country would come to dominate the others. Long gone was the notion of the balance of power as a guarantor of peace. Now, the balance of power was a fragile thing, with each of the great powers seeking to supplant its rivals in the name of security and prosperity. As a result, there was an ongoing, elaborate diplomatic dance as each power tried to shore up alliances, seize territory around the globe, and outpace the others.
While no great power deliberately sought war out, all were willing to risk war in 1914. That was at least in part because no politician had an accurate idea of what a new war would actually be like. The only wars that had occurred in Europe between the great powers since the Napoleonic period were the Crimean War of the 1850s and the wars that resulted in the formation of Italy and Germany in the 1850s, 1860s, and early 1870s. While the Crimean War was quite bloody, it was limited to the Crimean region itself and it did not involve all of the great powers. Likewise, the wars of national unification were relatively short and did not involve a great deal of bloodshed (by the standards of both earlier and later wars). In other words, it had been over forty years since the great powers had any experience of a war on European soil, and as they learned all too soon, much had changed with the nature of warfare in the meantime.
In the summer of 1914, each of the great powers reached the conclusion that war was inevitable, and that trying to stay out of the immanent conflict would lead to national decline. Germany was surrounded by potential enemies in France and Russia. France had cultivated a desire for revenge against Germany ever since the Franco-Prussian War. Russia feared German power and resented Austria for threatening the interests of Slavs in the Balkans. Great Britain alone had no vested interest in war, but it was unable to stay out of the conflict once it began.
In turn, the thing that inflamed jingoism and resentment among the great powers had been imperialism. The British were determined to maintain their enormous empire at any cost, and the Germans now posed a threat to the empire since Germany had lavished attention on a naval arms race since the 1880s. There was constant bickering on the world stage between the great powers over their colonies, especially since those colonies butted up against each other in Africa and Asia. Violence in the colonies, however, was almost always directed at the native peoples in those colonies, and there the balance of power was squarely on the side of Europeans. Thus, even European soldiers overseas had no experience of facing foes armed with comparable weapons.
The nature of nationalism had changed significantly over the course of the nineteenth century as well. Not only had conservative elites appropriated nationalism to shore up their own power (as in Italy and Germany), but nationalistic patriotism came to be identified with rivalry and resentment among many citizens of various political persuasions. To be a good Englishman was to resent and fear the growth of Germany. Many Germans came to despise the Russians, in part thanks to the growth of anti-Slavic racism. The lesser powers of Europe, like Italy, resented their own status and wanted to somehow seize enough power to join the ranks of the great powers. Nationalism by 1914 was nothing like the optimistic, utopian movements of the nineteenth century; it was hostile, fearful, and aggressive.
Likewise, public opinion mattered in a way it had never mattered earlier for the simple fact that every one of the great powers had at least a limited electorate and parliaments with at least some real power to make law. Even Russia, after a semi-successful revolution in 1905, saw the creation of an elected parliament, the Duma, and an open press. The fact that all of the powers had representative governments mattered, because public opinion helped fan the flames of conflict. Newspapers in this era tended to deliberately inflame jingoistic passions rather than encourage rational calculation. A very recognizably modern kind of connection was made in the press between patriotic loyalty and a willingness to fight, kill, and die for one’s country. Since all of the great powers were now significantly (or somewhat, in the case of Russia) democratic, the opinions of the average citizen mattered in a way they never had before. Journalism whipped up those opinions and passions by stoking hatred, fear, and resentment, which led to a more widespread willingness to go to war.
Thanks to the nationalistic rivalry described above, the great powers sought to shore up their security and power through alliances. Those alliances were firmly in place by 1914, each of which obligated military action if any one power should be attacked. Each great power needed the support of its allies, and was thus willing to intercede even if its own interests were not directly threatened. That willingness to go to war for the sake of alliance meant that even a relatively minor event might spark the outbreak of total war. That is precisely what happened.
In 1914, two major sets of alliances set the stage for the war. German politicians, fearing the possibility of a two-front war against France and Russia simultaneously, concluded an alliance with the Austrian Empire in 1879, only a little over a decade after the Prusso-Austrian War. In turn, France and Russia created a strong alliance in 1893 in large part to contain the ambitions of Germany, whose territory lay between them. Great Britain was generally more friendly to France than Germany, but had not entered into a formal alliance with any other power. It was, however, the traditional ally and protector of Belgium, which British politicians considered a kind of toehold on the continent. Finally, Russia grew increasingly close to the new nation of Serbia, populated as it was by a Slavic people who were part of the Eastern Orthodox branch of Christianity. The relationships between Great Britain and Russia with Belgium and Serbia, respectively, would not have mattered but for the alliance obligations that tied the great powers together.
Those alliances were now poised to mobilize armies of an unprecedented size. All of the great powers now fielded forces of a million men or more. Coordinating that many troops required detailed advanced planning and a permanent staff of high-ranking officers, normally referred to as the "general staff" of a given army. In the past, political leaders had often either led troops themselves or at least had significant influence in planning and tactics. By the early twentieth century, however, war plans and tactics were entirely in the hands of the general staffs, meaning political leaders would be obliged to choose from a limited set of "pre-packaged" options given to them by their generals.
Thus, when the war started, what took all of the leaders of the great powers - from the Kaiser in Germany to the Tsar in Russia - by surprise was the ultimatums they received from their own generals. According to the general staffs, it was all or nothing: either commit all forces to a swift and decisive victory, or suffer certain defeat. There could be no small incremental build ups or tentative skirmishes; this was about a total commitment to a massive war. An old adage has it that “generals fight the last war,” basing their tactics on what worked in previous conflicts, and in 1914 the “last war” most members of general staffs looked to was the Franco-Prussian War, which Prussia had won through swift, decisive action and overwhelming force.