The conflict developed on several fronts in Europe, Africa, and Asia. The two main scenarios were the Western front, where the Germans confronted Britain, France and, after 1917, the Americans. The second front was the Eastern front in which the Russians fought against Germans and Austro-Hungarians.

We can find several phases :

1. The war of movements
2. The Trench warfare or war of attrition
3. Changes in 1917
4. Final stage

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Germany had a designed plan to defeat its enemies very quickly: the Schlieffen Plan which main objective was to defeat the French Army with an enveloping movement and after the victory over France Germany could use all its military resources to destroy the Russian army before the Tsar could mobilise his massive troops.

So Germany attacked to France trough the Belgian border but the plan failed because of the French resistance in the Marne ( the first battle of the Marne) in the fall of 1914, and the Russians also halted the German advance in the East.

The military lines were stopped and the armies were prepared for a long war making trenches . The whole western front was dug with trenches and the armies waited behind them in a war of attrition. During this period many battles were fought in order to destroy the resistance of the enemy:

• Battle of Verdun (February-March 1916). The French led by the Marshall Pétain managed to defeat the Germans and block any of their attacks.
• Battle of Somme (July - November 1916). It was the first battle where the tank was used.  It was a battle with a high amount of casualties on both two sides but the front hardly moved.

Several changes transformed the evolution of the war :

- April of 1917 USA declared the war to Germany. This meant a big amount of soldiers and militar material for te Allies .

- November of 1917 The Russian Revolution provoked the abandon of the war by the new communist government. The Treaty of Brest Litovsk  ( 3 of March of 1918) signed the end of the war in the East with a lot of land won by Germany at the expense of the new Republic of Russia.

 During the year several offensives were made , first the German army , led by the marshal Ludendorf , attacked to the allied front but was stopped by the French army in the second battle of the Marne .

After this offensive the German army was exhausted and the renewed allied army counterattacked and the Germans was forced to leave from France.

After this defeat the Central Powers started to surrender

• Bulgaria surrendered once it signed the Armistice of Thessalonica on 29 September 1918.
• The Ottoman Empire surrendered on 30 October 1918 in the Armistice of Mudros.
• Austria-Hungary surrendered in the Armistice of Villa-Giusti (3 November 1918).
• A revolution broke out in Germany and  William II of Germany abdicated on 9 November and the Weimar Republic was proclaimed. The new German government surrendered and signed the Armistice of Compiègne on the 11th of  November.