The Anglo-Spanish War: Overview
Cromwell's Protectorate in alliance with France against Spain
After the ending of the Anglo-Dutch war in April 1654, Lord-Protector Cromwell and the Council of State turned their attention to England's traditional enemies France and Spain, which were at war with one another in the Spanish Netherlands. French and Spanish revulsion at the execution of King Charles I had given way to pragmatism, and both nations sought an alliance with the increasingly powerful English Protectorate. Throughout 1654, the ambassadors Antoine de Bordeaux-Neufville of France and Alonso de Cardenas of Spain vied with one another to secure Cromwell's favour.
Most members of the Council of State favoured an alliance with France, though a minority, headed by John Lambert, argued that the loss of trade with Spain would be too high a price to pay. Cromwell eventually decided to support France, initially through a commercial treaty rather than a military alliance. Although he had apparently abandoned the idea of intervening in the European war, Cromwell secretly planned the Western Design, an attack on Spanish territories in the West Indies, which was put into operation in 1655 and resulted in the capture of Jamaica by England. Meanwhile, the English fleet imposed an unofficial blockade to prevent supplies and reinforcements sailing from Spain to the West Indies.
War was openly declared in October 1655 and endorsed when the Second Protectorate Parliament assembled the following year. The blockade of Spain by the English navy continued during 1656-7 and severely disrupted the Spanish economy. In March 1657, England and France entered a formal military alliance against Spain during which English troops served alongside the French under Marshal Turenne in Flanders. Under the terms of the alliance, the port of Dunkirk was ceded to England after the Anglo-French victory over the Spanish at the battle of the Dunes in June 1658.
The war between France and Spain ended with the signing of the Peace of the Pyrenees on 28 October 1659. After the Restoration of Charles II to the throne of the Three Kingdoms, the Anglo-Spanish war was formally terminated in September 1660. Charles sold Dunkirk back to Louis XIV in November 1662 — though less than £300,000 of the promised half million was ever paid. Jamaica remained a British colony; the Spanish formally recognised Britain's ownership of the island in 1670.
or see related overview in the Military thread: the First Anglo-Dutch War