It is noteworthy that the birth of modern international law was associated with the origin of these juridical controversies as to the freedom of the sea.[610] It was the appearance of _Mare Liberum_ in 1609 that heralded the dawn of the new epoch. The little book of Grotius was at once a reasoned appeal for the freedom of the seas in the general interest of mankind, and the source from which the principles of the Law of Nations have come. The main reasons why the controversy broke out at that time and the pleas of Grotius had so much success are not difficult to discover. The period was characterised by a great expansion of commercial enterprise. The Western Powers of Europe, and above all the United Provinces, were pushing into every sea for the sake of traffic and gain. In some directions the trading adventurers found their way barred by claims to _mare clausum_ and monopoly of trade; in other directions it was open to them only under heavy burdens and aggravating restrictions. The northern seas, in theory at least, were closed to the whaling vessels engaged in what was then a most valuable business; and commerce and fishing within them were permitted only under irksome conditions. The passage through the Sound into the Baltic was subjected to high dues by Denmark; Venice claimed dominion in the Adriatic and levied imposts for the right of navigation there, and Genoa followed her example in the Ligurian Sea. But it was not so much the claim of Denmark to the sovereignty of the northern seas, or the rights asserted by Venice in the Adriatic, that led to the outburst for the freedom of the sea and of commercial intercourse at the beginning of the seventeenth century. Except with regard to English traffic with Iceland and Norway and the fishing there, more or less regulated by treaties, the Scandinavian claim at this time was not of great practical importance; and the dominion of Venice over the Adriatic was generally regarded as beneficial on the whole, by interposing a powerful barrier to the further extension of the Turkish empire in Europe, and by facilitating the suppression of pirates and Saracens.[611] It was the extravagant pretensions of Spain and Portugal to a monopoly of navigation and commerce with the New World and the East Indies that constituted the great obstacle to the new spirit of commercial enterprise. Founding their title on the Bulls of the Pope, and the right of discovery, conquest, and prior occupation, they arrogated to themselves the exclusive sovereignty of the great oceans which were the pathways to these immense regions,--the Atlantic, the Indian Ocean, and parts of the Pacific. Thus, as Grotius remarked, the whole Ocean except a little was to remain under the control of two nations, and all the other nations of the earth were to content themselves with the remnant.