What was the immediate cause of the First World War?

(i) The Sarajevo incident is the immediate cause of the First World War. On 28 June 1914, the Austrian Archduke Francis Ferdinand and his wife were shot dead in Sarajevo, the capital of Bosnia.
(ii) Austria saw the hand of Serbia behind the assassination of the Prince and served Serbia with an ultimatum. Due to the support of Russia, Serbia refused to accept the demands. So Austria declared a war on Serbia.