John Fiske, too, in the second volume of his "Historical Essays," dwells upon the causes of the enormous development of piracy in the seventeenth century. Speaking of the struggle of the Netherlands and England against the greatest military power of the world, he said that the former had to rely largely and the latter almost exclusively, upon naval operations, and continued: "Dutch ships on the Indian Ocean and English ships off the American coasts effectually cut the Spaniard's sinews of war. Now in that age ocean navigation was still in its infancy, and the work of creating great and permanent navies was only beginning. Government was glad to have individuals join in the work of building and equipping ships of war, and it was accordingly natural that individuals should expect to reimburse themselves for the heavy risk and expense by taking a share in the spoils of victory. In this way privateering came into existence and it played a much more extensive part in maritime warfare than it now does. The navy was but incompletely nationalized. Into expeditions that were strictly military in purpose there entered some of the elements of a commercial speculation, and as we read them with our modern ideas we detect the smack of buccaneering." England in dealing leniently with these buccaneers sailing under her flag, argued that since the gold and silver carried from America to Spain in Spanish ships was used to defray the expenses of a war which threatened her, English mariners were justified in capturing these vessels and seizing such treasures. But there is little doubt that by this interpretation the doors were opened wide to all sorts of trickery and outrage, carried on regardless whether the countries under whose flags both captors and captured sailed were at the time at war or at peace. Thus the naval and commercial restrictions, which Spain imposed upon other countries, proved at the end a boomerang, which did irreparable loss to Spain itself.