Do you think that it would be possible for a country to forget that it was in a war? It does sound as if it would be impossible, but it is something that has actually happened, and it led to the conflict being seen as the longest war in the history of the world.
The war itself was between the Dutch and the Isles of Scilly, which do exist, and the war lasted for a total of 335 years and 19 days. The history books state that there were no casualties in the war. It was the Dutch that completely forgot that they were indeed at war until a historian reminded them of it in 1985. They then decided that it was best to bring things to an end so they signed a peace treaty with the Isles of Scilly the following year therefore, bringing to a close the longest war ever.