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 ) . World War I . The war drew in all the world 's economic great powers , assembled in two opposing alliances : the Allies ( based on the Triple Entente of the Russian Empire , the French Third Republic , and the United Kingdom of Great Britain and Ireland ) versus the Central Powers of Germany and Austria-Hungary .