On the Eastern Front, the vast eastern plains and limited rail network prevented a trench warfare stalemate, though the scale of the conflict was just as large as on the Western Front. The Middle Eastern Front and the Italian Front also saw heavy fighting, while hostilities also occurred at sea, and for the first time, in the air.

At the start of the war, the Austro-Hungarian army was divided, the smaller division attacked Serbia while the larger division fought against the massive Russian army. The 1914 invasion of Serbia was a disaster. By the end of the year the Austrian army had taken no territory and had lost 227,000 men.

In May 1915, Italy joined the Allies and attacked Austria-Hungary. The bloody battle on the Italian Front would last for the next three-and-a-half years. It was only on this front that the Austrians proved effective in war, holding back the numerically superior Italian troops in the Alps.

The states of Germany, Austria-Hungary, the Ottoman Empire and Bulgaria, which fought against the Allies, were called the Central Powers because they were all located between the Russian Empire in the east and France and the U.K. in the west.

The war began on August 3, 1914 when Germany declared war on France, saying that France had infringed upon Germany’s territory. The day after this declaration of war Germany moved soldiers into Belgium. The Belgians resisted, but three days later the Germans captured the stronghold of Liege and Belgium fell. By August 18, the German army had overrun all of Belgium and was gathering on the French border to begin the offensive. Two days later the attack began, and the French were almost immediately driven out of Lorraine.

The war caused the disintegration of four empires: the Austro-Hungarian, the German, the Ottoman and the Russian. Germany lost its colonial empire and states such as Czechoslovakia, Estonia, Finland, Latvia, Lithuania, Poland and Yugoslavia gained independence.

The cost of waging the war set the stage for the breakup of the British Empire as well and left France devastated for more than a generation.

The Ottoman Empire (also known as the Turkish Empire or Turkey) took part in the Middle Eastern theatre of World War I, under the terms of the Ottoman-German Alliance. The alliance was established between the Ottoman Empire and the German Empire on August 2, 1914. It was this binding alliance that ultimately led the Ottoman Empire to join the Central Powers.

Both Germany and the Allies, hoping for an ally in the Balkans had secretly wooed Bulgaria. But Bulgaria decided in favour of the Germans and declared war on Serbia on October 11, 1915, hoping to annex the Serbian province of Macedonia. By October 21, Bulgarian troops had taken the Macedonian capital of Skopje, and had made contact with French forces on the Salonika Front. Three days later, the Bulgarian army had driven a wedge between the Allied forces in Greece and the Serbian army they were trying to reach.

World War I marked the end of the world order which had existed since the Napoleonic Wars, and later played an important part in the outbreak of World War II.