While England was combating Spain's claims in western waters, a new maritime power, the Netherlands, was breaking down the monopoly of Portugal in the east. The ships of the Dutch East India Company won their way against the Portuguese and made prize of their vessels. It was apparently to set at rest the consciences of members of the company who hesitated to pocket profits that had not been won in peaceful trade, that the Dutchman Grotius wrote his treatise on the law of prize, one chapter of which, under the title _Mare Liberum_, was published as an independent work. The book claimed the seas as a free highway for the ships of all nations, and freedom of trade for all nations on every sea. That age was not ready to accept either claim in its entirety. Two Englishmen, Welwod and Selden, wrote books to vindicate England's traditional sovereignty over the British seas, the limits of which no one was quite certain about. Even the British admirals who were supposed to defend British authority there, could never get the Crown lawyers to pronounce exactly on the point, some holding that British seas extended to the English settlements in America, others being satisfied with a line drawn from Norway to Cape Finisterre. Charles I set out, with his ship money fleets, to supplement the discourses of his subjects by "the louder language of a powerful navy." But it was left for his great successor, Cromwell, to use this latter language effectively, and to wring from the Dutch the concession that their ships should strike flag and topsail in the narrow seas. They always insisted, however, that this was done in courtesy, not as a recognition of British sovereignty over any part of the high seas. International incidents arising from the refusal of French captains to salute occurred until England relinquished her claim during the Napoleonic wars. * * * * * As to freedom of trade, the English Navigation Laws stood as a witness that Spain's policy of monopolizing colonial trade was considered worthy of emulation. Such monopolies were carefully guarded, as in Elizabeth's day, and as in her day efforts were made to break them down. To Cromwell's request that Englishmen be allowed liberty of conscience and of trade in the West Indies, the Spanish ambassador replied that it was to ask his master's two eyes. Thereupon Cromwell stopped asking, but despatched a fleet to the West Indies to seize a post which might become a centre of British trade.