Frantic competition among European powers marked the late 1800s and early 1900s. The strength of a nation was measured by the scope of its wealth and resources, the amount of land it held, and the size of its army and navy. The leaders of many countries believed that a nation could only achieve its political and economic goals if it had a strong military, a belief known as militarism. Conscript armies grew in most countries, in which young men were required to undergo a year or two of military training and were then sent home as reserves to be mobilized or called to action when needed for fighting. Naval budgets increased every year, especially in Great Britain and Germany. No country wanted to be without allies if war broke out, so two major military alliances took hold. Germany, fearful of being hemmed in by enemies on its east and west, signed an agreement with Austria-Hungary to support each other in a European war. Russia and France reached a similar agreement.

Militarists increasingly viewed their nations' armed forces as above criticism. And many greatly admired such military values as self-sacrifice, discipline, and obedience. War was increasingly seen as an adventure, an opportunity to fight and even die for one's country. Karl Pearson, a British writer at the time, claimed that wars are necessary. He maintained that nations could establish their rightful position in the world "by contest, chiefly by way of war with inferior races, and with equal races by the struggle for trade routes and for the sources of raw materials and food supply."

Others held similar views. Count Theobald von Bethmann Hollweg, the chancellor of Germany at the turn of the twentieth century, claimed that "the old saying still holds good that the weak will be the prey of the strong. When a people will not or cannot continue to spend enough on armaments to be able to make its way in the world, then it falls back into the second rank."

For Pearson, Hollweg, and other Europeans, a nation was more than a country. To them, the members of a nation not only shared a common history, culture, and language but also common ancestors, character traits, and physical characteristics. Many believed, therefore, that a nation was a biological community and that membership in it was passed on from one generation to the next. In other words, belief in a nation was similar to what many believed about race.

Some historians refer to Europe in the early 1910s as a powderkeg (a barrel of gunpowder). European nations were eager for war to prove their superiority over other nations. They had growing militaries. And they had joined together to form opposing military alliances, pledging to support their partner nations in case of war. Like a barrel of gunpowder, the smallest spark could make everything explode.

The spark that set off World War I came on June 28, 1914, when a young Serbian patriot shot and killed Archduke Franz Ferdinand, the heir to the Austro-Hungarian Empire (Austria), in the city of Sarajevo. The assassin was a supporter of the Kingdom of Serbia, and within a month the Austrian army invaded Serbia. As a result of the military alliances that had formed throughout Europe, the entire continent was soon engulfed in war. Because European nations had numerous colonies around the world, the war soon became a global conflict..