1.ASSASSINATION IN SAREJEVO:

On 8th june 1914,Archduke Franz Ferdinand,the heir to Austrianthrone and his wife Sophie were assassinated in sarejevo.The murder was committed by a young Bosnian student Gavrilo Princip with the support of a secret serb organization called the Black Hand.The Black Hand was formed with the aim of realizing the nation ideal ,i.e union of all serbs.However the Serbian Government didn't support it much as it was too radical.The assassination of Archduke and his wife activated the alliances that were already in place.Germany responded quickly and assured Austria Hungary of full support .Austriapresented Serbia with stiff ultimatum  with the following demands-:

               1.Apologies to Austria -Hungary.

               2.Dismissal of all officials whom Austria objected to.

               3. An explanation for assassination of Archduke and his wife.

               4.Participation of Austrian officials in inquiry .

               5.Austrian police be allowed to enter Serbia,s territory.

Serbians accepted all demands except the one of allowing Austrian officials participate within Serbian territory,in investigation of crimes.Austria-Hungary declared war on Serbia.Russia supported Serbia and went on to mobilise its forces .Germany issued an ultimatum to Russia demanding her to stop mobilizing its forces.When no reply was received from Russians ,Germany declared war on Russia and on France .Germany then went on to invade the neutral Belgium and as a result Britain declared war on Germany.