The four main causes of World War One is–
(1) Germany has become a great industrial country and wanted to have more markets for trade. (2) Germany was jealous of the colonial and naval greatness of England. William II, Kaiser of Germany, was very ambitious and wanted to gain influence in Turkey by linking Berlin with Baghdad by a railway line. This gave rise to a great rivalry between England and Germany. (3) The immediate cause of the war the murder of Archduke Ferdinand (the heir to the throne of the Austrian Empire) at Sarajevo by a Serbian. The Austrian held the Government of Serbia responsible for the murder and ultimately attacked Serbia.
Germany, Austria, Hungary, Turkey and Bulgaria were on one side and, were called Central Powers. England, France, Serbia, Belgium, Japan, Russia were on the other side and were called the Allies. Italy in 1915 and the U.S.A. in 1917 joined the Allies against the Central Powers.
The war started on the 4th August 1914 and ended on 11th November 1918.