Under the terms of the Edict of Nantes (1598), Henri IV of France granted extensive rights to Protestant Huguenots at La Rochelle and other specified towns, thus bringing the long-running French Wars of Religion to an end. But Henri's successor Louis XIII, advised by Cardinal Richelieu, declared war on the Huguenots and in 1627, La Rochelle was besieged. Hoping to gain the support of English Protestants, King Charles I and his favourite the Duke of Buckingham decided to mount an expedition to lift the siege and liberate the Huguenots.
Buckingham himself took command of the force of 80 ships and 6,000 men that set sail from England on 27 June 1627. On 10 July, Buckingham's fleet anchored off the Isle of Rhé which controlled the approaches to La Rochelle. English troops fought their way ashore against strong opposition from the French, then laid siege to the fortress of Saint Martin, the main town on the island. By the end of September, the defenders of Saint Martin were close to starvation and seemed on the point of surrendering, but a French convoy fought its way through the English blockade and resupplied the fort.
The English were also running short of supplies yet King Charles diverted funds intended for the relief of the expedition to buy works of art that had become available from the Duke of Mantua's collection. In October 1627, with the weather worsening and French reinforcements arriving from the mainland, Buckingham decided on a desperate attempt to take the fortress by storm. The assault failed disastrously: the French had advance warning of the attack, the scaling ladders proved too short and the siege cannon had mistakenly been reloaded back onto the English ships. As the English retreated across a narrow causeway to the safety of the ships, the French attacked and inflicted terrible casualties. It was said that 4,000 of the 6,000 men who had set out from England died on the Isle of Rhé, either during the fighting or from disease . Buckingham had no choice but to abandon the siege and return to England.
In April 1628, while Members of King Charles' third Parliament were discussing their grievances, a second expedition set sail for La Rochelle. It was reluctantly commanded by the Earl of Denbigh. When he arrived at La Rochelle on 1 May 1628, Denbigh found French defences guarding the approach to the harbour and the Huguenot enclave besieged by French troops. Faced with sickness among his men, lack of supplies and a general lack of enthusiasm for the enterprise, Denbigh sailed straight back to England.
The Duke of Buckingham was blamed for all the nation's grievances, domestic and foreign. In London, citizens took to the streets to demonstrate against him, yet Charles continued to display absolute confidence in his favourite. They began planning a third expedition to La Rochelle.
Ignoring warnings about his personal safety, Buckingham travelled to Portsmouth to supervise the refitting of the fleet. On 23 August 1628, he was attacked and stabbed to death. His killer was John Felton, a mentally unstable lieutenant who had served on the Isle of Rhé expedition. Felton was arrested and hanged. Charles went into mourning for Buckingham, and was unable to understand why most of the nation celebrated his death with bonfires and rejoicing.