Claim: World War I involved one group of countries fighting another.

World War I -LRB- WWI or WW1 -RRB- , also known as the First World War , the Great War , or the War to End All Wars , was a global war originating in Europe that lasted from 28 July 1914 to 11 November 1918 . More than 70 million military personnel , including 60 million Europeans , were mobilised in one of the largest wars in history . Over nine million combatants and seven million civilians died as a result of the war -LRB- including the victims of a number of genocides -RRB- , a casualty rate exacerbated by the belligerents ' technological and industrial sophistication , and the tactical stalemate caused by gruelling trench warfare . It was one of the deadliest conflicts in history , and paved the way for major political changes , including revolutions in many of the nations involved and to WWII twenty-one years later .   The war drew in all the world 's economic great powers , assembled in two opposing alliances : the Allies -LRB- based on the Triple Entente of the Russian Empire , the French Third Republic , and the United Kingdom of Great Britain and Ireland -RRB- versus the Central Powers of Germany and Austria-Hungary . Although Italy was a member of the Triple Alliance alongside Germany and Austria-Hungary , it did not join the Central Powers , as Austria-Hungary had taken the offensive against the terms of the alliance . These alliances were reorganised and expanded as more nations entered the war : Italy , Japan and the United States joined the Allies , while the Ottoman Empire and Bulgaria joined the Central Powers .   The trigger for the war was the assassination of Archduke Franz Ferdinand of Austria , heir to the throne of Austria-Hungary , by Yugoslav nationalist Gavrilo Princip in Sarajevo on 28 June 1914 . This set off a diplomatic crisis when Austria-Hungary delivered an ultimatum to the Kingdom of Serbia , and entangled international alliances formed over the previous decades were invoked . Within weeks , the major powers were at war and the conflict soon spread around the world .   On 25 July Russia began mobilisation and on 28 July , the Austro-Hungarians declared war on Serbia . Germany presented an ultimatum to Russia to demobilise , and when this was refused , declared war on Russia on 1 August . Being outnumbered on the eastern front , Russia urged its Triple Entente ally France to open up a second front in the west . Back in 1870 , the Franco-Prussian war had ended the Second French Empire and ceded the provinces of Alsace-Lorraine to a unified Germany . Bitterness over their defeat and the determinance to retake Alsace-Lorraine made the acceptance of Russia 's plea for help an easy choice so France began full mobilisation on 1 August and on 3 August , Germany declared war on France . The border between France and Germany was heavily fortified on both sides so according to the Schlieffen Plan , Germany then invaded neutral Belgium and Luxembourg before moving towards France from the north , leading the United Kingdom to declare war on Germany on 4 August due to their violation of Belgian neutrality . After the German march on Paris was halted in the Battle of the Marne , what became known as the Western Front settled into a battle of attrition , with a trench line that changed little until 1917 . On the Eastern Front , the Russian army led a successful campaign against the Austro-Hungarians , but the Germans stopped its invasion of East Prussia in the battles of Tannenberg and the Masurian Lakes . In November 1914 , the Ottoman Empire joined the Central Powers , opening fronts in the Caucasus , Mesopotamia and the Sinai . In 1915 , Italy joined the Allies and Bulgaria joined the Central Powers ; Romania joined the Allies in 1916 , as did the United States in 1917 .   The Russian government collapsed in March 1917 , and a revolution in November followed by a further military defeat brought the Russians to terms with the Central Powers via the Treaty of Brest Litovsk , which granted the Germans a significant victory . After a stunning German offensive along the Western Front in the spring of 1918 , the Allies rallied and drove back the Germans in a series of successful offensives . On 4 November 1918 , the Austro-Hungarian empire agreed to an armistice , and Germany , which had its own trouble with revolutionaries , agreed to an armistice on 11 November 1918 , ending the war in victory for the Allies .   By the end of the war or soon after , the German Empire , Russian Empire , Austro-Hungarian Empire and the Ottoman Empire ceased to exist . National borders were redrawn , with several independent nations restored or created , and Germany 's colonies were parceled out among the victors . During the Paris Peace Conference of 1919 , the Big Four -LRB- Britain , France , the United States and Italy -RRB- imposed their terms in a series of treaties . The League of Nations was formed with the aim of preventing any repetition of such a conflict . This effort failed , and economic depression , renewed nationalism , weakened successor states , and feelings of humiliation -LRB- particularly in Germany -RRB- eventually contributed to the start of World War II .