whole question of invasion, which will be discussed in the next chapter. CHAPTER VI INVASION England has not been invaded since A.D. 1066, when, the country having no fleet in being, William the Conqueror effected a landing and subjugated the kingdom. During the eight centuries and more that have since elapsed, every country in Europe has been invaded and its capital occupied, in many cases more than once. It is by no means for lack of attempts to invade her that England has been spared the calamity of invasion for more than eight hundred years. It is not because she has had at all times--it may indeed be doubted if she has had at any time--organized military force sufficient to repel an invader, if he could not be stopped at sea. It is because she can only be invaded across the sea, and because whenever the attempt has been made she has always had naval force sufficient to bring the enterprise to nought. It is merely a truism to say that the invasion of hostile territory across the sea is a much more difficult and hazardous enterprise than the crossing of a land frontier by organized military force. But it is no truism to say that the reason why it is so much more difficult and more hazardous is that there is no real parallel between the two cases. I assume a vigorous defensive on the part of the adversary assailed in both cases--a defensive which, though commonly so called, is really offensive in its nature. The essential difference lies in this, that two countries which are separated by the sea have no common frontier. Each has its own frontier at the limit of its territorial waters, but between these two there lies a region common to both and from which neither can be excluded except by the superior naval force of the other.