European politics in the early 1900's had two sides. While some politicians thought war had been erased by progress, others influenced by a fierce arms race felt that war was inevitable. Germany felt war should happen now rather than later, while they still felt they had an advantage over Russia. Germany, fearing attacks from both France and Russia, developed the Schieffenplan, which involved a swift attack on France designed to destroy France early, so that they could then concentrate on Russia.
When Archduke Fran Ferdinand was assassinated by a Serbian activist, an ally of Russia, Austria-Hungary was given a promise of support from Germany. Russia supported Serbia, so Germany declared war on Russia. France and Britain then declared war on Germany. Declarations continued until most of Europe was at war with each other.
Germany made the decision to destroy the French at the battle of Verdun. There were some victories, but nothing that lasted, and a high number of casualties. Attempts to find another way into the enemy lands led to the failed invasion of Gallipoli, where allied forces were stopped by Turkish resistance. There was also conflict on the Italian front by the Balkans and the Middle East.
The only large naval engagement was the battle of Jutland where both sides declared victory. Germans decided to pursue USW (Unrestricted Submarine Warfare). This policy allowed submarines to attack any target they found, including those belonging to the neutral United States. This caused the U.S. to enter the war in 1917, supplying the allies with needed manpower. The war caused instability in Russia, leading to the revolutions of 1917, and the beginnings of socialist government. Russia surrendered on December 15.
Efforts by the Germans to take the offensive in the west failed. On November 11, 1918 Germany surrendered, becoming the last of the Central Powers to sign an armistice. Each of the defeated nations signed a treaty with the allies, called the Treaty of Versailles.