England's involvement in the Treaty of the Pyrenees is linked to its military alliance with France against Spain during the Thirty Years War, particularly under Oliver Cromwell's leadership in 1654. England aimed to secure Spanish territories in the West Indies, while France sought to expand its European borders at Spain's expense. The treaty, signed in 1659, primarily favored France, enhancing its territorial claims, while England acquired the port of Dunkirk. However, following the death of Cromwell in 1658 and the subsequent political instability under his son, England's interests were not effectively represented in the treaty negotiations. After the restoration of the Stuart monarchy in 1660, England made a separate peace with Spain and subsequently sold Dunkirk to France.