These examples will also serve to illustrate and enforce the second essential of this kind of war.  As has been already said, for a true limited object we must have not only the power of isolation, but also the power by a secure home defence of barring an unlimited counterstroke.  In all the above cases this condition existed.  In all of them the belligerents had no contiguous frontiers, and this point is vital.  For it is obvious that if two belligerents have a common frontier, it is open to the superior of them, no matter how distant or how easy to isolate the limited object may be, to pass at will to unlimited war by invasion.  This process is even possible when the belligerents are separated by a neutral State, since the territory of a weak neutral will be violated if the object be of sufficient importance, or if the neutral be too strong to coerce, there still remains the possibility that his alliance may be secured.

We come, then, to this final proposition—­that limited war is only permanently possible to island Powers or between Powers which are separated by sea, and then only when the Power desiring limited war is able to command the sea to such a degree as to be able not only to isolate the distant object, but also to render impossible the invasion of his home territory.

Here, then, we reach the true meaning and highest military value of what we call the command of the sea, and here we touch the secret of England’s success against Powers so greatly superior to herself in military strength.  It is only fitting that such a secret should have been first penetrated by an Englishman.  For so it was, though it must be said that except in the light of Clausewitz’s doctrine the full meaning of Bacon’s famous aphorism is not revealed.  “This much is certain,” said the great Elizabethan on the experience of our first imperial war; “he that commands the sea is at great liberty and may take as much or as little of the war as he will, whereas those that be strongest by land are many times nevertheless in great straits.”  It would be difficult to state more pithily the ultimate significance of Clausewitz’s doctrine.  Its cardinal truth is clearly indicated—­that limited wars do not turn upon the armed strength of the belligerents, but upon the amount of that strength which they are able or willing to bring to bear at the decisive point.

It is much to be regretted that Clausewitz did not live to see with Bacon’s eyes and to work out the full comprehensiveness of his doctrine.  His ambition was to formulate a theory which would explain all wars.  He believed he had done so, and yet it is clear he never knew how complete was his success, nor how wide was the field he had covered.  To the end it would seem he was unaware that he had found an explanation of one of the most inscrutable problems in history—­the expansion of England—­at least so far as it has been due to successful war.  That a small country with a weak army should have