The Ottoman Empire and Bulgaria joined the Central Powers (Germany and Austria-Hungary).

Italy, Romania, Greece, the United States of America, China and Japan joined the Allies of the Triple Entente.

In the Mediterranean, the British tried to take the Dardanelles Strait in order to isolate Turkey, but they were defeated at Gallipoli (1915-1916).

Britain took the German colonies in Africa, except in eastern Africa.

Japan conquered the German colonies in Asia.

With the help of Arab nationalists, the Allies occupied several Ottoman possessions in the Near East.

The world's great powers confronted each other, along with their empires. Other countries joined the war over time, making this a genuine world war:

• The Ottoman Empire and Bulgaria joined the Central Powers (Germany and Austria-Hungary).
• Italy, Romania, Greece, the United States of America, China and Japan joined the Allies of the Triple Entente.

Germany tried to execute the Schlieffen Plan, which was to defeat France quickly and then attack Russia. However, the French stopped the Germans at the Battle of the Marne. At France's request, Russia launched an offensive against Germany. This forced the Germans to move troops to the east, which saved France.

Defensive resources, like trenches or machine guns, were extremely effective and so the fronts stabilised. There were vast networks of trenches, where soldiers spent months in very harsh conditions.

In 1916, the Germans tried to break through the western front at the Battle of Verdun, and the British tried to do the same at the Battle of the Somme. However, neither side advanced far despite the deaths of hundreds of thousands of soldiers.

As the western front stabilised, the Allies attacked in other regions:

• In the Mediterranean, the British tried to take the Dardanelles Strait in order to isolate Turkey, but they were defeated at Gallipoli (1915-1916).
• Britain took the German colonies in Africa, except in eastern Africa. Japan conquered the German colonies in Asia.
• With the help of Arab nationalists, the Allies occupied several Ottoman possessions in the Near East.

There were also naval battles. The British fleet patrolled the coasts of Germany, and Germany counterattacked with submarine warfare.

1917 marked a turning point in the war. The Russian front collapsed because of the Bolshevik Revolution, which caused Russia to withdraw from the conflict. However, the decisive event was when the United States of America joined the war on the side of the Allies. This provided the Allies with significant amounts of supplies and soldiers, which enabled them to win the war.

In 1918, the Germans made peace with Russia via the Treaty of Brest-Litovsk. They moved their troops westwards and launched an attack. In response, the Allies attacked all fronts using tanks and planes. The Central Powers surrendered: first Turkey, then Austria, and finally Germany, following the abdication of Kaiser Wilhelm II. The armistice between Germany and the Allies was signed on 11th November 1918. World War I had come to an end.