What was the main reason for the start of world war 1

The main reason for the start of World War One was the assassination of Archduke Franz Ferdinand

Explanation:

 The assassination of Archduke Franz Ferdinand was the main reason for the start of ww1

Explanation: Many countries had alliances with each other and when he was assassinated, war was being used as a threat and since countries were in alliances they got involved with the conflict and that why it was call a world war.