I just read Tuchman's "Gun's of August". While she mentions the assassination of Austrian Archduke Franz Ferdinand, I interpreted her book to indicate that the causes of the war were multiple and that the assassination didn't really contribute that much to the start of hostilities.

Am I misunderstanding what she wrote, or are most statements about the effect of the assassination over-reaching?

In this article, makes it sound like Serbia was was belligerent and precipitated the whole thing. http://www.history.com/this-day-in-history/archduke-franz-ferdinand-assassinated