The infancy of the young prince, and the consequent victory of republican principles in the great assembly of 1651, made the danger from the House of Orange for the time imperceptible. When John de Witt became Grand Pensionary of Holland in 1653, the safety of the republic was threatened not by civil dissension but by foreign conquest. [Sidenote: =Quarrel between the United Provinces and England.=] With the restoration of order in England by the defeat of the king in the civil war had naturally come a considerable increase in commercial enterprise, and the Dutch traders became once more sensible of English rivalry and opposition in every part of the globe. To this natural rivalry gradually became added special causes of disagreement. During the interval between the defeat of the king and the reduction of the English possessions in the West Indies by the Parliament, the loyal colonists had preferred to trade with a foreign power whose chief was closely related to their king, rather than with the rebels of their own country who had imprisoned him. Consequently the Dutch had succeeded in withdrawing from English merchants the bulk of their American trade. To settle this matter and some others the Parliament sent to the Hague in May 1649 an envoy, Dr. Dorislaus, who had been one of the late king’s judges. While he was at the Hague in the character of ambassador, he was murdered by some of Montrose’s men by way of reprisal for the death of Charles I. In extreme anger at this insult St. John was sent in 1651 to demand from the estates general the expulsion of prince Charles and his adherents, and their consent to the union of the two republics under a common government, which should have its seat in England. [Sidenote: =The Act of Navigation, 1651.=] The estates general naturally refused to surrender on demand the independence which they had fought so hard to win, and in August 1651 the English Parliament passed the Act of Navigation which was in reality the signal for war. By this famous act the policy was first enunciated which was to govern the relations of the great maritime powers to their colonies for a century and a half, the policy namely which regarded colonies as the mere feeders of the mother country. It enacted that foreign ships might only import into England the products of the countries to which they belonged. [Sidenote: =War with England, 1651–1654.=] It was directed obviously against the Dutch, who were at that time the great carriers of the world, and was intended not only to destroy the trade of the Dutch with the English colonies, but also to enable the English ships to wrest the bulk of the carrying trade from their hands. War at once broke out, in which the genius of Blake and the superior guns of the English fleets triumphed over the tenacity of Tromp and the valour of Opdam. The Dutch merchant shipping was shut up behind the Texel. The English remained masters of the sea. Even the Portuguese dared to