The Three Hundred and Thirty Five Years' War

April 17, 1986:

The Three Hundred and Thirty Five Years' War between the Netherlands and the Isles of Scilly ends.
The Three Hundred and Thirty Five Years' War (Dutch: Driehonderdvijfendertigjarige Oorlog) was a war between the Netherlands and the Isles of Scilly (located off the southwest coast of Great Britain). It is said to have been extended by the lack of a peace treaty for 335 years without a single shot being fired, which would make it one of the world's longest wars and the war with the fewest casualties. Despite the uncertain validity of the declaration of war, peace was finally declared in 1986.
The origins of the war can be found in the Second English Civil War, fought between the Royalists and Parliamentarians from 1642 to 1652. Oliver Cromwell had fought the Royalists to the edges of the Kingdom of England. In the West of England this meant that Cornwall was the last Royalist stronghold. In 1648, Cromwell pushed on until mainland Cornwall was in the hands of the Parliamentarians.
The Royalist Navy was forced to retreat to the Isles of Scilly, which lie off the Cornish coast and were under the ownership of Royalist John Grenville.
The navy of the United Provinces of the Netherlands was allied with the Parliamentarians. The Netherlands had been assisted by the English under a number of rulers in the Eighty Years' War (1568–1648), starting with Queen Elizabeth I of England. The Treaty of Münster (30 January 1648) had confirmed Dutch independence from Spain. The Netherlands sought to maintain their alliance with England and had chosen to ally with what seemed would be the victorious side in the Civil War.
The Dutch Navy was suffering heavy losses from the Royalist fleet based in Scilly. On 30 March 1651, Admiral Maarten Harpertszoon Tromp arrived in Scilly to demand reparation from the Royalist fleet for the Dutch ships and goods taken by them.
According to Whitelocke's Memorials (cited in Bowley, 2001), a letter of 17 April 1651 explains: "Tromp came to Pendennis and related that he had been to Scilly to demand reparation for the Dutch ships and goods taken by them; and receiving no satisfactory answer, he had, according to his Commission, declared war on them".
As most of England was now in Parliamentarian hands, war was declared specifically upon the Isles of Scilly.
In June 1651, soon after the declaration of war, the Parliamentarian forces under Admiral Robert Blake forced the Royalist fleet to surrender. The Netherlands fleet, no longer under threat, left without firing a shot. Due to the obscurity of one nation's declaration of war against a small part of another, the Dutch did not officially declare peace.
In 1985, Roy Duncan, historian and Chairman of the Isles of Scilly Council, wrote to the Dutch Embassy in London to dispose of the myth that the islands were still at war. Embassy staff found the myth to be accurate and Duncan invited the Dutch ambassador Jhr. Rein Huydecoper to visit the islands and sign a peace treaty. Peace was declared on 17 April 1986, 335 years after the "war" began. The Ambassador joked that it must have been harrowing to the Scillonians "to know we could have attacked at any moment."

Ok, that's just stupid. Hopefully, we won't be at war in Afghanistan that long, but you never know.  Unfortunately, there have been a lot of casualties in Afghanistan.