The incident that triggered the beginning of World War 1 was the assassination of the heir to the Austro-Hungarian throne.
Archduke Ferdinand
German submarine warfare
The assassination of archduke Ferdinand
The assassination of Archduke Franz Ferdinand of Austria, which led to the outbreak of World War I ----
He was killed in Sarajevohttp://en.wikipedia.org/wiki/Archduke_Franz_Ferdinand_of_Austria
June 28, 1914.
After the start of World War II.
Poland, on 1 September 1939
The war is generally accepted to have begun on 1 September 1939, with the invasion of Poland Slovakia
The assassination of Archduke Franz Ferdinand of Austria-Hungary by Serbian nationalists.
The shooting of the Archduke of Austro-Hungarian Franz Ferdinand.