There really isn't a short history of WWII that doesn't oversimplify everything. Americans commonly believe that the war started on December 7, 1941 when the
Anyhow, it doesn't pay to consider the war as an isolated incident anyway, given that it grew directly out of the punitive clauses of the Versailles Treaty, which in turn was France's revenge for their humiliating defeat during the Franco-Prussian War. So you might as well take it as the last act of the Franco-Prussian Wars that started in 1871. When did it end? The consensus is that it was all over on V-J Day in 1945 when the Japanese signed the articles of surrender on board the USS Missouri, but Berlin remained an occupied city by the four Great Powers until the Berlin Wall fell at the hands of impatient Berliners in 1989. So technically, that's when it was really all over, over there.
EDIT: Wow, more topical and timely than I thought. Lo, Clive Davis gives Senator Obama a rhetorical kick in the ass in the Spectator, reminding him that "There were, in fact, some isolated outbreaks of fighting before Pearl Harbour." LOL.