For the latter he turned to a man who had won a military reputation in the Civil War second only to that of the great Oliver himself, Robert Blake, colonel of militia. Blake was chosen as one of three "generals at sea" in 1649. As far as is known he had never before set foot on a man of war; he was a scholarly man, who had spent ten years at Oxford, where he had cherished the ambition of becoming a professor of Greek. At the time of his appointment he was fifty years old, and his entire naval career was comprised in the seven or eight remaining years of his life, and yet he so bore himself in those years as to win a reputation that stands second only to that of Nelson among the sea-fighters of the English race. Blake made short work of Rupert's cruising and destroyed the Royalist pretensions to Jersey and the Scillies. One of his rewards for the excellent service rendered was a position in the Council of State, in which capacity he did much toward the bettering of the condition of the sailors, which was one of the striking reforms of the Commonwealth. His test, however, came in the first Dutch War, in which he was pitted against Martin Tromp, then the leading naval figure of Europe. In the wars with Spain, English and Dutch had been allies, but the shift of circumstances brought the two Protestant nations into a series of fierce conflicts lasting throughout the latter half of the 17th century. The outcome of these was that England won the scepter of the sea which she has ever since held. The main cause of the war was the rivalry of the two nations on the sea. There were various other specific reasons for bad feeling on both sides, as for instance a massacre by the Dutch of English traders at Amboyna in the East Indies, during the reign of James I, which still rankled because it had never been avenged. The English on their side insisted on a salute to their men of war from every ship that passed through the Channel, and claimed the rights to a tribute, of all herrings taken within 30 miles off the English coast. Cromwell formulated the English demands in the Navigation Act of 1651. The chief of these required that none but English ships should bring cargoes to England, save vessels of the country whence the cargoes came. This was frankly a direct blow at the Dutch carrying trade, one to which the Dutch could not yield without a struggle.