archduke Franz Ferdinand of Austria was assinated. Austria-Hungary wanted to punish Serbia for the muder. Russia formed an army to help Serbia. Triple Alliance or Central powers were Germany, Austria-Hungary, and italy. Triple entente or Cental powers were france, great britian, and russia. Germany declared ware on russia and france. Germany invaded belgium to get at france and GB joined. Was a trench ware that had machine guns, rifles, poison gas, flame throwers, landmind, tanks. etc. America joined after Germany sunk more us ships. in 1917 3 years after war began.