I believe this instance taken from an actual occurrence says everything. I need not add one word.
The wedge which Alsace pushed into Germany near Weissenburg separated South Germany from North Germany more effectively than the political line of the Main. It needed a high degree of determination, national enthusiasm, and devotion for our South German allies not to hesitate one moment but to identify the danger of North Germany with their own and to advance boldly in our company, in spite of that other danger in their own immediate proximity to which a clever conduct of the war on the part of France would have exposed them. That France in her superior position had been ready to yield to the temptation, which this advanced outpost of Strassburg offered her against Germany, whenever her internal affairs made an excursion into foreign lands desirable, we had seen for many decades. It is well known that the French ambassador entered my office as late as August 6, 1866, with the briefly worded ultimatum: "Either cede to France the city of Mayence, or expect an immediate declaration of war." I was, of course, not one moment in doubt about my reply. I said to him: "Well, then, it is war." He proceeded with this reply to Paris. There they changed their mind after a few days, and I was given to understand that this instruction had been wrung from Emperor Napoleon during an attack of illness. The further attempts on Luxembourg and the consequent issues are known to you. I will not revert to them, nor do I believe that it is necessary to prove that France did not always show a sufficiently strong character to resist the temptations which the possession of Alsace brought with it.
The question was, how to secure a guarantee against this. It had to be of a territorial nature, because the guarantees of foreign powers were not of much use to us, such guarantees having at times been subject to supplementary and attenuating declarations. One might have thought that all Europe would have felt the need of preventing the ever recurring wars of two great and civilized peoples in the heart of Europe, and that it would have been natural to assume that the simplest way to do this was to strengthen the defences of that one of the two participants who doubtless was the more pacific. I cannot, however, say that at first this idea appeared convincing everywhere. Other expedients were looked for, and the suggestion was often made that we should be satisfied with an indemnity and the razing of the French fortresses in Alsace and Lorraine. This I always opposed, because I considered it an impracticable means of maintaining peace. The establishment of an easement on foreign territory is very oppressive and disagreeable to the sense of sovereignty and independence of those who are affected by it. The cession of a fortress is felt scarcely more bitterly than the injunction by foreigners not to build on the territory which is under one's own sovereignty. French passions have probably been excited more frequently and more successfully by a reference to the razing of that unimportant place of Hüningen than by the loss of any conquered territory which France had to suffer in 1815. I placed, therefore, no confidence in this means, especially since the geographical configuration of this advanced outpost--as I took the liberty of calling it--would have put the starting place for the French troops just as near to Stuttgart and Munich as it had always been. It was important to put it farther back.