opportunity to declare war on Sweden. Although it was the depth of
winter Charles Gustavus lost no time in attacking Denmark. He quickly
drove the Danes from Schonen and Funen and invaded Seeland. Frederick
was compelled at Roeskilde (February, 1658) to accept the terms of the
conqueror. Denmark became virtually a Swedish dependency, and undertook
to close the Sound to all foreign ships. Involved as the republic was in
disputes at this time with both France and England, and engaged in war
with Portugal, De Witt would have been content to maintain a watchful
attitude in regard to Scandinavian matters and to strive by diplomacy to
secure from Sweden a recognition of Dutch rights. But his hand was
forced by Van Beuningen, who went so far as to urge the Danish king to
rely on his defensive alliance with the republic and to break the treaty
of Roeskilde. Charles Gustavus promptly invaded Denmark, drove the
Danish fleet from the sea, placed strong garrisons at Elsinore and
Kronborg, and laid siege to Copenhagen. Van Beuningen had proudly
asserted that "the oaken keys of the Sound lay in the docks of
Amsterdam," and his boast was no empty one. At the beginning of October
a force of thirty-five vessels under Obdam carrying 4000 troops sailed
for the Sound with orders to destroy the Swedish fleet, and to raise the
siege of Copenhagen. On November 8 Obdam encountered the Swedes in the
entrance to the Baltic. The Swedish admiral Wrangel had forty-five ships
under his command, and the battle was obstinate and bloody. Obdam
carried out his instructions. Only a remnant of the Swedish fleet found
refuge in the harbour of Landskrona, but the Dutch also suffered
severely. The two vice-admirals, Witte de With and Floriszoon, were
killed, and Obdam himself narrowly escaped capture, but Copenhagen was
freed from naval blockade.

Charles Gustavus however held military possession of a large part of
Denmark, and in the spring began to press the attack on the capital
from the land side. As both England and France showed a disposition to
interfere in the conflict, the States-General now acted with unexpected
vigour, recognising that this question to them was vital. An imposing
force of seventy-five warships, carrying 12,000 troops and mounting 3000
guns, was despatched in May, 1659, under De Ruyter to the Baltic.
Negotiations for peace between the Scandinavian powers under the
mediation of France, England and the United Provinces, were now set o