The 335 Year War (as it is now known) was a bloodless conflict between the Netherlands and the tiny Isles of Scilly which began as far back as 1651 during the English Civil War.
The Dutch, an unlikely player in this domestic clash, had decided to join the conflict on the side of the Parliamentarians after identifying them as the most likely victors. The Royalists – long time allies of the Dutch – considered this decision a betrayal and set about punishing their former friends by raiding Dutch shipping lanes in the English Channel.
By 1651 however, things were not going well for Charles and his Royalist forces. After a series of successful battles, Cromwell had pushed Charles' army back to their last stronghold of Cornwall, whilst the Royalist navy had been forced back to the tiny Isles of Scilly.
The Dutch, seeing an opportunity to recoup some of their losses from the Royalist raids, immediately sent a fleet of twelve warships to the Isles of Scilly to demand reparations. After receiving no satisfactory answer from the Royalists, the Dutch Admiral Maarten Tromp subsequently declared war on the Isles of Scilly on the 30th March 1651.
Interestingly, there are conflicting accounts over whether or not Tromp actually had the authority to declare war on the Isles of Scilly. Some argue that Tromp had been given the authority prior to setting out, whilst others argue that he carried out a blockade of the islands whilst waiting for his government's approval. Regardless of the specifics, three months later in June 1651 Cromwell's forces under the command of Admiral Robert Black forced the Royalist fleet to surrender and the Isles of Scilly reverted to Parliamentarian control. The Dutch fleet subsequently sailed home, albeit forgetting to declare peace on the poor little Isles of Scilly!
Fast forward to 1985 when a local Scilly historian called Roy Duncan wrote to the Dutch Embassy in London to see if there was any evidence to support the seemingly absurd claim of a 335 year war. To everyone's surprise, the embassy uncovered a series of documents which suggested that the Netherlands and the Islands were, indeed, still at war!
Perhaps concerned with the possibility of a renewed Dutch threat, Duncan hastily wrote to the Dutch ambassador Rein Huydecoper inviting him to visit the islands and to sign a peace treaty. Huydecoper agreed, and on the 17th April 1986 a peace treaty was signed between the Isles of Scilly and the Kingdom of the Netherlands.