World War I lasted from 28 July 1914 to 11 November 1918, a period of about 4 years and 3.5 months (4 years and 106 days). The war began with Austria- Hungary's declaration of war on Serbia and ended with the Armistice of 11 November 1918, when Germany signed an agreement to cease hostilities, marking the effective end of fighting
. The armistice came into effect at 11 a.m. on 11 November 1918, known as Armistice Day, and brought an end to combat on the Western Front and other theaters of the war
. Although the fighting stopped then, formal peace treaties, such as the Treaty of Versailles, were signed later (in 1919), and some conflicts and political changes continued after the armistice
. In summary, World War I lasted just over four years, from late July 1914 until the armistice in November 1918
