Dee ihe na-aga n'ihu maka paragraf a - Ogbugbu nke Archduke Franz Ferdinand nke Austria na 28 June 1914 na Sarajevo site n'aka Gavrilo Princip, onye otu nke Young Bosnia nzukọ, dugara Austria-Hungary ikwusa agha megide Serbia, na 28 July 1914. Agha obodo ahụ bịara ka njọ mgbe Germany busoro Russia agha ma wakpo France na Belgium, si otú ahụ dọrọ Great Britain banye n'agha nke ghọrọ Agha Ụwa Mbụ. Serbia meriri n'agha ukwu ndị mbụ nke Agha Ụwa Mbụ, gụnyere Agha Cer, na Agha Kolubara
, na-egosi mmeri mbụ ndị Allied meriri ndị Central Powers na Agha Worldwa Mbụ.