Great Britain defended her course by stating the premise that a blockade was an allowable expedient in war--which the United States did not question--and upon that premise reared a structure of argument which emphasized the wide gap between British and American interpretations of international law. A blockade being allowable, Great Britain held that it was equally allowable to make it effective. If the only way to do so was to extend the blockade to enemy commerce passing through neutral ports, then such extension was warranted. As Germany could conduct her commerce through such ports, situated in contiguous countries, almost as effectively as through her own ports, a blockade of German ports alone would not be effective. Hence the Allies asserted the right to widen the blockade to the German commerce of neutral ports, but sought to distinguish between such commerce and the legitimate trade of neutrals for the use and benefit of their own nationals. Moreover, the Allies forebore to apply the rule, formerly invariable, that ships with cargoes running a blockade were condemnable. On the chief point at issue Sir Edward Grey wrote: "The contention which I understand the United States Government now puts forward is that if a belligerent is so circumstanced that his commerce can pass through adjacent neutral ports as easily as through ports in his own territory, his opponent has no right to interfere and must restrict his measure of blockade in such a manner as to leave such avenues of commerce still open to his adversary. "This is a contention which his Majesty's Government feel unable to accept and which seems to them unsustained either in point of law or upon principles of international equity. They are unable to admit that a belligerent violates any fundamental principle of international law by applying a blockade in such a way as to cut out the enemy's commerce with foreign countries through neutral ports if the circumstances render such an application of the principles of blockade the only means of making it effective." In this connection Sir Edward Grey recalled the position of the United States in the Civil War, when it was under the necessity of declaring a blockade of some 3,000 miles of coast line, a military operation for which the number of vessels available was at first very small: "It was vital to the cause of the United States in that great struggle that they should be able to cut off the trade of the Southern States. The Confederate armies were dependent on supplies from overseas, and those supplies could not be obtained without exporting the cotton wherewith to pay for them. "To cut off this trade the United States could only rely upon a blockade. The difficulties confronting the Federal Government were in part due to the fact that neighboring neutral territory afforded convenient centers from which contraband could be introduced into the territory of their enemies and from which blockade running could be facilitated.