Complex sentence: Archduke Franz Ferdinand of Austria and his wife Sophie, Duchess of Hohenberg were assassinated on 28 June 1914 in Sarajevo, and Austria-Hungary declared war on Serbia on 28 July 1914.
Split into simpler sentences: Archduke Franz Ferdinand of Austria and his wife Sophie, Duchess of Hohenberg were assassinated on 28 June 1914 in Sarajevo. Subsequently Austria-Hungary declared war on Serbia on 28 July 1914.