Who was responsible for the outbreak of this war? Why the politicians of course! Then monarchs were still notable political figures, and had a considerable impact in the war that followed. These were a few of the more famous politicians of the period.
Wilhelm was the king of Germany in 1914, and some historians suggest he was a big factor in the outbreak of the war. Certainly, the assassination of the Archduke had little to do with Germany or Wilhelm; but the kaiser threw his support behind Austria-Hungary in the emerging war in the Balkans.
Soon after the kaiser duly declared war not only with Russia, but France as well. There was little negotiation or open discussion between the empires. Germany's military hierarchy had drafted a plan before the war that outlined how the army could defeat both France and Russia in Europe. To begin with, most within the German Empire supported the war, which the Germans expected to win fairly quickly.
German's king was also commander in chief of the army. Although it was largely left to his chief military advisers Ludendorff and Hindenburg to draft military plans for the war. They not could bring the expected victory in Western Europe at least; although their army was very effective in the East where it made considerable advances.
After the United States joined the war, and Germany's shattering defeat at the Battle of Amiens in 1918, it became clear that the Germans could not win the war. As such, the Germans began peace talks in which the Entente requested the abdication of Wilhelm as a precursor for an armistice. With most within Germany calling for an end to the war, Wilhelm duly abdicated shortly before the November 11 armistice.
Many in France, Britain and the United States considered the German king a war criminal. However, no subsequent war tribunal trials were held, except in Leipzig. Thus, little substantial evidence materialized in the postwar period.
President Woodrow Wilson
In 1917, President Wilson could no longer ignore World War One after German U-boats resumed unrestricted submarine warfare to wipe out British merchant ship supplies. That much ensured that U.S. ships were once again in the firing line of U-boats, and further losses of American sailors at sea. Wilson addressed Congress to declare war with the German Empire, so the United States entered the war alongside Britain and France.
The impact of Wilson's support for the Entente was not immediate. The United States still had to get its army together and amass troops in France. By 1918, the Americans joined the fray and provided the British and French with considerable reinforcements in the West. Buoyed by U.S. support, the coalition began a series of advances in France that shattered Germany's lines and ensured the full retreat of its army.
Wilson laid the foundations for peace talks with Germany based on his "14 Points" speech in 1918. That encouraged the Germans to open peace discussions with the Entente in 1918 as their army retreated. In 1918, the German chancellor sent a note to Wilson calling for an armistice based upon the 14 points. As such, the president was certainly influential in ending the war with a victory for the Entente.
At the Paris Peace Conference, Wilson established the League of Nations. This was the forerunner of the modern-day United Nations. He also provided input for the postwar treaties drafted, such as the Treaty of Versailles. However, as the Treaty of Versailles was not approved by Congress, the United States did not join the League.
Clemenceau emerged as France's prime minister in 1917. Upon his election, he rallied France to maintain the front with Germany. In 1918, France and its allies turned the war around after halting a series of rapid enemy advances. More substantial advances from the French, British and U.S. Army followed. The Germans retreated beyond the Hindenburg Line, so an armistice was established.
Clemenceau was influential in the Paris Peace Conference. It were here that he outlined peace terms for the defeated German Empire within the Versailles Treaty. Clemenceau, and much of France, believed that Germany caused the war. As such, Clemenceau insisted the Treaty of Versailles include substantial reparations, the return of Alsace-Lorraine to France and the wholesale reduction of the German military. Those were just a few of the treaty's provisions, which remained a little controversial because it was not ratified by Congress.
Lenin was the Bolshevik Party's most prominent campaigner who did not support Russian involvement in WWI. But in 1917 the party remained exiled in Switzerland until the king of Russia abdicated. After the collapse of the Romanov dynasty, in February, Lenin won over the support of the German High Command. Among Lenin's policy pledges were peace in Russia and an armistice with Germany that would ensure greater reinforcements for the German army in the West. As such, he was given a railway passage to return to Russia.
When Lenin returned to Petrograd, he distributed the April Thesis. The thesis promised peace to the Russian people. That gained greater support for his party, and in October the Bolsheviks seized the Winter Palace. Then the Bolsheviks established the communist regime, and began peace talks with the Germans that continued into 1918. The Treaty of Brest-Litovsk ended the war in Eastern Europe, but the Russians surrendered considerable territory to the Germans. Thus, Lenin had abandoned Russia's former Entente allies; and there were no Bolsheviks at the Paris Peace Conference.
These politicians were influential during WWI. Not all of them caused the war, with the likes of Wilson and Lenin both restoring peace in Europe. However, Europe's monarchies within Germany, Austria-Hungary and Russia were swept aside during a war.