Following the Austro-Prussian War, there were forces within Prussia urging for an annexation of territory from Austria - namely Bohemia (but not Moravia) and Austrian Silesia. Bismarck opposed this as he did not want to make a permanent enemy of Austria.
But what if Bismarck hadn't been able to satiate these nationalist elements Prussia had annexed these territories?
Part of the reason for the OTL annexation of Alsace-Lorraine was to make up for not annexing territory from Austria. German nationalists will clamor for Alsace-Lorraine, but perhaps Germany doesn't take the territory TTL?