<P> In November 1918, the Allies had ample supplies of men and materiel to invade Germany . Yet at the time of the armistice, no Allied force had crossed the German frontier; the Western Front was still some 720 kilometres (450 mi) from Berlin; and the Kaiser's armies had retreated from the battlefield in good order . These factors enabled Hindenburg and other senior German leaders to spread the story that their armies had not really been defeated . This resulted in the stab - in - the - back legend, which attributed Germany's defeat not to its inability to continue fighting (even though up to a million soldiers were suffering from the 1918 flu pandemic and unfit to fight), but to the public's failure to respond to its "patriotic calling" and the supposed intentional sabotage of the war effort, particularly by Jews, Socialists, and Bolsheviks . </P> <P> The Allies had much more potential wealth they could spend on the war . One estimate (using 1913 U.S. dollars) is that the Allies spent $58 billion on the war and the Central Powers only $25 billion . Among the Allies, the UK spent $21 billion and the U.S. $17 billion; among the Central Powers Germany spent $20 billion . </P> <P> In the aftermath of the war, four empires disappeared: the German, Austro - Hungarian, Ottoman, and Russian . Numerous nations regained their former independence, and new ones were created . Four dynasties, together with their ancillary aristocracies, all fell as a result of the war: the Romanovs, the Hohenzollerns, the Habsburgs, and the Ottomans . Belgium and Serbia were badly damaged, as was France, with 1.4 million soldiers dead, not counting other casualties . Germany and Russia were similarly affected . </P> <P> A formal state of war between the two sides persisted for another seven months, until the signing of the Treaty of Versailles with Germany on 28 June 1919 . The United States Senate did not ratify the treaty despite public support for it, and did not formally end its involvement in the war until the Knox--Porter Resolution was signed on 2 July 1921 by President Warren G. Harding . For the United Kingdom and the British Empire, the state of war ceased under the provisions of the Termination of the Present War (Definition) Act 1918 with respect to: </P>

When did the first world war start and why