The Warring Parties of World War I

The Russian Empire was unwilling to allow Austria–Hungary to eliminate its influence in the Balkans, and supported its long time Serb protégés. France, sporting significant animosity over the German conquest of Alsace-Lorraine during the Franco-Prussian War ordered French mobilization. The United Kingdom declared war on Germany, following an 'unsatisfactory reply' to the British ultimatum that Belgium must be kept neutral.

The Triple Entente (from French entente - "agreement") was the name given to the alliance between the United Kingdom, the French Third Republic, and Russia after the signing of the Anglo-Russian Entente in 1907. The Franco-Russian Alliance, along with the Anglo-Russian Entente and the Entente Cordiale, formed the Triple Entente between the British Empire, France and Russia. This was an effective deterrent to the Triple Alliance of the Central Powers. The Central Powers was the term used to describe the wartime alliance of Germany and Austria-Hungary against the Allies. Later the term was extended to include Turkey and Bulgaria. 

President Wilson, who had previously claimed neutrality, called for the arming of U.S. merchant ships delivering munitions to combatant Britain, for supporting the British blockading of German ports and mining of international waters, and for preventing the shipment of food from America and elsewhere to combatant Germany. After German submarines sank seven U.S. merchant ships, Wilson called for war on Germany, which the US Congress declared on 6 April 1917.

In March 1917, demonstrations in Petrograd culminated in the abdication of Tsar Nicolas II and the appointment of a Provisional Government. This arrangement led to confusion and chaos both at the front and at home. The army became increasingly ineffective. The war and the government became increasingly unpopular. Discontent led to a rise in popularity of the Bolshevik Party, led by Vladimir Lenin. He promised to pull Russia out of the war and was able to gain power. The triumph of the Bolsheviks in November was followed in December by an armistice and negotiations with Germany.

The new government acceded to the Treaty of Brest-Litovsk on 3 March 1918. It took Russia out of the war and ceded vast territories, including Finland, the Baltic provinces, parts of Poland and Ukraine to the Central Powers.

With the adoption of the Treaty of Brest-Litovsk, the Entente no longer existed. The Allied powers led a small-scale invasion of Russia, partly to stop Germany from exploiting Russian resources and, to a lesser extent, to support the "Whites" (as opposed to "Reds") in the Russian Civil war. 

With the aid of U.S. troops, the badly beaten and continually harassed German troops fell back in rapid retreat.

     While Germany was staggering under the continual offensive of the Allied armies, the German allies were suffering even greater misfortunes. They surrendered one by one.

World War I ended with the armistice on 11 November 1918. The United States, the greatest economic beneficiary of the war, helped make the peace, but with its rejection of the Treaty of Versailles refused responsibility for maintaining it.