The Concert of The Hague (1659): England, France, and the Dutch Republic Chart a Path to Peace
On May 21, 1659, diplomats representing the Dutch Republic, the Commonwealth of England, and the Kingdom of France signed the Concert of The Hague, a joint statement outlining how the Second Northern War should be resolved. The agreement called for Sweden and Denmark–Norway to make peace on terms rooted in the 1658 Treaty of Roskilde, while guaranteeing free navigation through the Danish Sound and the Baltic Sea. Though not a treaty imposed on the belligerents themselves, the Concert proved remarkably influential, laying groundwork that the eventual Peace of Copenhagen would largely follow.
A Baltic War Draws in the Great Powers
By the late 1650s, the Second Northern War had transformed from a regional conflict into a crisis threatening the balance of power across Europe. Sweden's King Charles X Gustav had already forced Denmark into the harsh Treaty of Roskilde in February 1658, stripping away the provinces of Scania, Halland, Blekinge, and Bornholm, along with Trøndelag in Norway. Rather than settling for these gains, Charles X Gustav renewed his assault on Denmark that August, laying siege to Copenhagen itself. A Swedish conquest of Denmark risked giving Stockholm total control over the Sound, the narrow strait linking the Baltic to the North Sea, through which passed vital trade in grain, timber, and naval stores. The Dutch Republic, whose merchant fleets depended on unimpeded Baltic access, could not tolerate such an outcome and sent a fleet that fought the Battle of the Sound in October 1658 to relieve the besieged Danish capital. England, still governed as a Commonwealth following Oliver Cromwell's death in September 1658, and France, Sweden's traditional ally, both had stakes in how the conflict resolved. By spring 1659, representatives of all three powers gathered at The Hague to hammer out a shared position designed to end the fighting on terms acceptable to the wider European community.
Did You Know?
The Concert of The Hague drew its commercial terms from the 1656 Treaty of Elbing, a Swedish-English agreement, showing how a bilateral trade deal from three years earlier ended up shaping a three-power peace framework for the entire Baltic region.
Negotiating the Concert
The negotiations at The Hague brought together seasoned diplomats navigating competing loyalties. The Dutch delegation, closely tied to Grand Pensionary Johan de Witt, pushed hardest for guarantees protecting free navigation of the Sound, a matter of direct commercial survival for Amsterdam's merchants. French envoys, mindful of Paris's alliance with Sweden, sought to preserve Swedish gains where possible, while English representatives weighed both trade interests and the shifting priorities of a Commonwealth government in transition. Despite these different starting points, the three powers reached consensus on May 21, 1659. They agreed that any lasting peace between Sweden and Denmark–Norway should be built upon the framework already established at Roskilde, rather than reopening the entire territorial settlement from scratch. Crucially, they insisted that navigation rights through the Sound and the Baltic follow the model set out in the 1656 Treaty of Elbing, which had granted commercial powers guaranteed access to Baltic ports. This blending of Roskilde's territorial terms with Elbing's commercial guarantees gave the Concert its distinctive character: a settlement that accepted Sweden's regional gains while safeguarding the trading interests of the maritime powers who had brokered the deal.
From Concert to the Peace of Copenhagen
The Concert of The Hague was not a peace treaty binding Sweden and Denmark directly; it was a statement of intent by outside powers determined to shape the conflict's outcome. Fighting continued for nearly another year, with Charles X Gustav's death in February 1660 removing the war's most aggressive architect and opening the door to serious negotiations. When Swedish and Danish representatives finally concluded the Peace of Copenhagen on May 27, 1660, the terms closely mirrored what the three mediating powers had outlined at The Hague thirteen months earlier. Denmark permanently ceded Scania, Halland, and Blekinge to Sweden, cementing Swedish control over the Baltic's southern approaches, but recovered Trøndelag and Bornholm, which Roskilde had also stripped away. Free navigation through the Sound was preserved, satisfying the Dutch Republic's central demand. The episode demonstrated how mid-seventeenth-century great powers, even those with sharply divergent alliances, could coordinate diplomatic pressure to contain a regional war before it destabilized the wider European trading system. The Concert of The Hague thus stands as an early example of collective great-power diplomacy shaping the outcome of a conflict its signatories were not directly fighting.