World War I’s origins were in the Serbian nationalists under Austrian-Hungarian rule. These nationalists wanted freedom for the Serbs from foreign rule. This movement was called pan-slavism and was primarily aimed at freeing the Serbs and creating a new independent country for them.
In the West, France wanted certain territories back from Germany, and was nursing grievances against it. Therefore, Germany, with the French on one side and the Russians (allies of the Serbs) on the other, began to fear encirclement and a two-front war. A two-front war would be a situation in which Russia and France would fight as allies against Germany.
The prime minister of Germany, Otto von Bismarck, in anticipation of a two-front war, made an alliance with Russia—a re-insurance treaty. He also made alliances with Austria (1879) and Italy (1882). Italy however, later broke this treaty and joined France, Britain and Russia.
However, Emperor William II of Germany took away Bismarck’s power and withdrew from their alliance with Russia.
Soon Britain began to fear that Germany was becoming too large and powerful and joined in an alliance with Russia and France against Germany just as Bismarck had feared. This alliance was called the Triple Entente.
A main event that led to World War I was the Bosnian Crisis (1908-1909). Two Slavic states were annexed to Austria-Hungary, a devastating blow to the enterprising nationalist Serbs. Russia, being an ally of the Serbs, wanted to fight Austria, but Germany threatened war with Russia if they marched on Austria. Russia backed down, not being strong enough to resist German troops.
The situation therefore, by 1914, the eve of World War I, was the following. Serbia was supported by Russia against Austria-Hungary and Germany. The Triple Entente (Britain, France and Russia, later joined by Italy) was against Germany and its allies.
The last blow dealt was the assassination of Archduke Franz-Ferdinand of Austria and his wife Sophia on June 28th, 1914. The Archduke and his wife were killed by a member of the Black Hand, a group formed by the nationalist Serbs. The Archduke had wanted to bring Slavic countries under Austrian rule and form a greater power than Austria-Hungary.
World War I was now about to break out, even though no one anticipated how devastating it would really be.