The immediate cause of World War I was the assassination of Archduke Ferdinand, heir to the throne of Austria-Hungary. Shortly after, Austria-Hungary declared war on Serbia. This event caused the mobilization of French and Russian troops. Sensing French and Russian involvement in this conflict, Germany backed its ally Austria-Hungary and declared war on France and Russia. England became involved in the war when German troops passed through Belgium, a neutral country and an ally of England. Germany had violated Belgium neutrality in the war and England had to defend the country. A little while after the start of the war Italy joined the war on the side of the Triple Alliance. This is how the alliance system played a major role in the involvement of the major European powers in the war.
In the late nineteenth century and early twentieth century one of the most important areas of the world was the Balkan Peninsula which was controlled by the Ottoman Empire. The Balkan Peninsula had crucial trade routes to European countries as well as India and Africa and had many different and diverse people and cultures living in this region setting off conflicts and tensions.
In 1848 a Pan-Slav Congress was set up which wanted to unite all the people of Slavic heritage. This created problems because so many people of Slavic heritage lived in Austria-Hungary or the Ottoman Empire which controlled the Balkan Peninsula. The first tensions in this region came in 1877 during the Russo-Turkish War. In the war between Russia, Serbia, and the Ottoman Empire, the Ottoman Empire lost and was forced to give up a lot of its territory in the Balkans including Bulgaria, and Bosnia-Herzegovina, Montenegro, and Romania. In the treaty of San Stefano, Bulgaria and Bosnia-Herzegovina which were made into autonomous states. In addition the treaty gave more land and power to Russia and Serbia in the Balkan Peninsula.
In 1912 Bulgaria, Russia and Serbia formed a treaty and successfully attacked the Ottoman Empire for control of the Balkan Peninsula. The only territory that remained in the hands of the Ottoman Empire at the end of the war was Constantinople. In 1913 another war was fought involving Serbia and the territory in the Balkans. Serbia attacked Bulgaria and won, gaining even more land. These two wars are known as the Balkan Wars. In addition, Serbia also took land that bordered Bosnia-Herzegovina. These moves made by Serbia were made to create a Greater Serbia, powerful enough to attack the Austria-Hungary Empire and take back Bosnia which Austria-Hungary had been given in the Congress of Berlin.
The tensions on the Balkan Peninsula created great conflict and tensions that involved the Ottoman Empire, Austria, Russia, and Serbia over the course of several years leading up to World War I.