On 28 June, Archduke Franz Ferdinand, heir to the Austrian-Hungarian throne, and his wife were shot dead in the streets of Bosnia's capital, Sarajevo. As the Archduke and the Duchess of Hohenburg, rode in an open car, on an official visit of the city, a Bosnian student known as Gavrilo Princip lunged at the car, firing at the archduke's neck and his wife, Sophie's stomach, killing the couple.

The 19-year-old assassin surrendered almost immediately. A member of a nationalist group from neighboring Serbia, Princip said that he was revenging the oppression of the Serbian people. This act would start World War I.

Serbia was backed by Russia - and by France and Britain, Russia's partners in the Triple Entente. Germany (hesistantly) backed its Austrian ally. When diplomacy failed, Austria-Hungary declared war on Serbia on July 28.

Russia mobilized its troops the next day; Germany, fearing a threat on its eastern border, declared war on Russia on August 1. On August 3, after France began to mobilize, Germany declared war on that nation as well, invading Luxembourg, announcing their intention to march through neutral Belgium on the way to France. This spurred Britain to declare war on Germany on August 4. Within a month, Montenegro was fighting on the side of Serbia, Japan on the side of its ally Britain, while Turkey had taken up arms for its Teutonic benefactors (mostly German). Gradually, nation after nation was sucked into the conflict. Soon the greatest war the world had ever seen for more than 100 years was raging on three continents.

Related link: See The path to World War I

By November, the war had reached a stalemate after the German advance on Paris was stopped at the river Marne. Battle-weary troops dug hundreds of kilometres of defensive trenches which stretch across Europe from the North Sea to Switzerland.

Enemy trenches are separated by a muddy no-man's-land strewn with water-filled craters, barbed wire and unclaimed bodies. Forays by either side simply added to the lengthy casualty lists. Commanders were unable to find a way to break the deadlock.

Meanwhile, life in the trenches was nightmarishly monotonous. Most of the soldiers' time was spent waiting -- either to be sent "over the top" to attack enemy lines, a task likely to end in injury or death, or for the next assault.

The trenches were warrens of slippery mud populated by rats. It was almost impossible to stay dry and some soldiers developed "trench foot", a fungal disease caused by permanently wet feet. Men passed the time by writing letters home, mending their clothes, telling jokes -- an digging more trenches.

Conditions were so bad that a rota system was developed. Soldiers spent about one week in every four on the front line. The rest of their time was spent in the reserves.