The conquests of France in the southern Netherlands caused great anxiety to the Dutch; and the high-handed action of French pirates in searching and seizing Dutch merchantmen in the Mediterranean aroused much indignation.  The States, acting on De Witt’s advice, replied by sending a squadron under De Ruyter to put a stop to these proceedings.  The Dutch admiral took vigorous action and captured some French freebooters.  The French government thereupon forbade Dutch vessels to enter French harbours.  The Dutch replied by a similar embargo and threatened to blockade the French coast.  This threat had the desired effect, and an accommodation was reached.  The peace of the Pyrenees in 1659, by which the French retained a large part of their conquests in Flanders, Hainault and Namur, while the English acquired possession of Dunkirk, was disquieting.  For the relations with England, despite the goodwill of the Protector, were far from satisfactory.  The trade interests of the two republics clashed at so many points that a resumption of hostilities was with difficulty prevented.  More especially was this the case after the outbreak of war with Portugal in November, 1657.

The Dutch accused the Portuguese government of active connivance with the successful revolt of the Brazilian colonists against Dutch rule.  What was once Dutch Brazil was now claimed by the Lisbon government as a Portuguese possession, and De Witt demanded an indemnity.  As this was not conceded, a squadron under Obdam, November, 1657, blockaded the Portuguese coast, while another under De Ruyter made many seizures of merchant vessels.  Cromwell was disposed to intervene, but his death on September 3,1658, removed any fears of English action.  Meanwhile the Dutch captured Ceylon and Macassar and practically cut off Portuguese intercourse with the East Indies.  At last in August, 1661, a treaty was signed by which the Dutch abandoned all territorial claims in Brazil, but were granted freedom of trade and an indemnity of 8,000,000 fl. to be paid in sixteen years, and, what was more valuable, they retained possession of their conquests in the East.

The protracted dispute with Portugal was however of quite subordinate importance to the interest of the Dutch in the complications of the so-called Northern War.  On the abdication of Christina in 1654, Charles X Gustavus had succeeded to the Swedish throne.  The new king was fired with the ambition of following in the footsteps of Gustavus Adolphus, and of rendering Sweden supreme in the Baltic by the subjection of Poland and Denmark.  Charles was a man of great force of character and warlike energy, and he lost no time in attempting to put his schemes of conquest into execution.  Having secured the alliance of the Great Elector, anxious also to aggrandise himself in Polish Prussia, the Swedish king declared war against Poland, and in the early summer of 1656 laid siege to Danzig.  But the importance of the Baltic trade