Considering the Germans pretty much invented the things, what if, during the Franco-Prussian War, the Germans had developed a couple of proto-Zeppelins & decided to try them out just to see what happens. Afterall there's no better way to test military equipment than during an actual war. So they use these proto-Zeppelins during the Seige of Paris...
What effect, if any, does the use of these Zeppelins have upon the population of Paris?
But more importantly, what effect does the introduction of Zeppelins have upon warfare in general - for example: would WWI see everyone operate Zeppelins?
And what of aircraft? If everyone had invested in Zeppelins, could have the development of aircraft be delayed?
Anything else?