From 30 March 1651 to 17 April 1986 there was a war between the Dutch and the Isles of Scilly. Now it is known as the three hundred and thirty five years war.
Back in 1651, the last year of the English civil war, King Charles and his army had been forced back to Cornwall and his navy forced back to the Isles of Scilly. the Dutch, who were on the side of Oliver Cromwell (who eventually won), sent 12 ships to Scilly. They were hoping to receive reparations from the Royalist navy. They were denied and so declared war on the Isles of Scilly on 30th March 1651 (although some historians dispute this because the Dutch Admiral may not have had the power to declare war). 3 months later, in June 1651, the Dutch sailed back home after the Royalist fleet surrendered. However, the Dutch sailed home forgetting to declare peace on the Isles of Scilly.
Then, in 1985, a Scilly historian called Roy Duncan wrote to the Dutch embassy in London to check for evidence of the war. The embassy found documents that showed evidence of the Netherlands and the Isles of Scilly still being at war. Duncan then invited the Dutch ambassador Rein Huydecoper to come to the islands and sign a peace treaty. He signed the treaty on the 17th of April 1986, marking the end of the longest ever war.