Mezue ahịrịokwu na-esonụ: 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 ndị mbụ nke Agha Worldwa Mbụ, gụnyere Agha nke Cer, na
Agha nke Kolubara, na-egosi mmeri mbụ nke ndị Allied megide Central Powers na Agha Worldwa Mbụ.