How did the assassination lead to War?

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How did the assassination lead to War?
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• In June 1914 Archduke Franz Ferdinand, the heir
  to the Austro-Hungarian throne was assassinated
  while visiting Sarajevo, the capital of Bosnia.
  This spark off a process that led to war
  throughout Europe within a few weeks.
• The Austrians blamed Serbia for the assassination
  and, after issuing an ultimatum, Austria declared
  war on Serbia.
• Because of the Alliance System, Russia supported
  Serbia, and Germany supported Austria.
• Within six weeks of the assassination, the great
  countries of Europe were at war.

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• 28 June 1914 The heir to the Austro-Hungarian
  throne, Archduke Franz Ferdinand is assassinated
  in Bosnia.
• Austria blames Serbia for the killing of Archduke
  Franz Ferdinand.
• Austria declares war on Serbia. Belgrade (in
  Serbia) is shelled.
• The Russian army gets ready to help Serbia defend
  itself against the Austro-Hungarian attack.
• Germany, Austrias ally, sends a demand to Russia
  ordering it to hold back from helping Serbia.
• Germany declares war on Russia. It also begins
  to move its army towards France, Russias ally.
• The French army is put on a war footing, ready to
  fight a German invasion.
• Germany declares war on France and invades
  neutral Belgium. Britain orders Germany to
  withdraw from Belgium.
• The Germans are still in Belgium, so Britain
  declares war on Germany.
• To complete the picture, Austria declares war on
  Russia.