Why did the Prussians decide to declare a unified German Empire after the Franco-Prussian war instead of any other time?

by electon100

I have been researching German history during the 19th century recently, but none of the books I've read explain why the Franco-Prussian war led to a "unified" Germany in a way that I can understand other than that patriotism was high at that point. Can anyone explain this or at least point me in the direction of some sources that will help me out? Thanks in advance.

elos_