To understand the origins of World War I, you need to understand the rise of Germany to Great Power status. Through the nineteenth century, under the leadership of Otto von Bismarck, the kingdom of Prussia increasingly gained power within the German Confederation. Victory over France in the Franco-Prussian War resulted in the creation of a single unified Germany.

With this in mind, you should keep two factors in mind: first, before 1871, Germany did not exist as a unified polity, and secondly, its very creation was tied with the national humiliation of France. Other European Great Powers could not help but notice that the European balance of power had been broken with this moment. In response, Bismarck set up a Triple Alliance with Austria-Hungary and Italy. This would, however, lead to the creation of counter-alliances against Germany's growing power.

Meanwhile, Germany sought to exert power and political influence abroad as it entered into the European race for colonies while also building up its military power. In this respect, long before the start of the First World War, you have a long history of building tensions among the European Great Powers, which were fed by a combination of imperialism, militarism and nationalism. Meanwhile, within Austria-Hungary (Germany's ally), you can observe nationalism as a force for political disintegration, such as when Archduke Franz Ferdinand was assassinated by Serbian nationalists. This act was blamed on Serbia (which had the support of Russia) by Austria-Hungary blamed Serbia. This political crisis between Serbia and Austria-Hungary had the effect of activating these alliance systems, resulting in the First World War.