Some events are inevitable. After the Franco-Prussian War World War I became inevitable. It was only a matter of time and Bismarck himself feared that a great war will happen soon. (But it took longer than he thought.)
Do not forget that France always had a problem with its neighbors. For along time Austria (the other European hegemonial power) was a problem for France, because Austria and Spain (both ruled by different branches ofHouse Hapsburg) surrounded France. That's the reason France was interested in both the Spanish succession and in driving Austria out of the Netherlands. After Austro-Prussian war Prussia became a problem for France because Prussia managed to unite most of Germany and to defeat Austria (who had been a guarantor that the German Confederation stayed powerless). Remember that the French battle cry in the Franco-prussian War was 'Revenge for Sadowa!'. And that means revenge for the Austrian defeat at Königsgrätz (a name unpronouncable in French, thus Sadowa, which is near Königsgrätz, was chosen).
Even if Bismarck had found another way of creating the German Empire, France would have tried everything to keep Germany powerless. And that would have led to war (which until World War I was always the common way to solve diplomatic problems). Thus a Franco-German(!) War was inevitable.