World War I involved one group of countries fighting another.
The Allies of World War I , or Entente Powers , were the countries that opposed the Central Powers in the First World War . The Central Powers ( Mittelmächte Központi hatalmak İttifak Devletleri or Bağlaşma Devletleri Централни сили Tsentralni sili ) , consisting of Germany , , the Ottoman Empire and Bulgaria -- hence also known as the Quadruple Alliance ( Vierbund ) -- was one of the two main factions during World War I ( 1914 -- 18 ) . The Paris Peace Conference , also known as Versailles Peace Conference , was the meeting of the Allied victors , following the end of World War I to set the peace terms for the defeated Central Powers diplomats from more than 32 countries and nationalities . World War I . During the Paris Peace Conference of 1919 , the Big Four ( Britain , France , the United States and Italy ) imposed their terms in a series of treaties .