So I've just discovered Russia and Japan are still at war as they never signed the WW2 treaty. They are apparently hoping to get all 4 of the islands seized during the war back, but only 2 of them were specified in the treaty thus they did not sign. Though they did having a meeting regarding this last year.
There is also Syria and Israel which seems to be just due to hatred and unwillingness to negotiate with the Golan Heights.
So I am wondering if there are any other countries in the same vein? If the reason is known for the lack of a peace treaty would also be appreciated!
Also I would describe prolonged war in this context as being officially at war with no combat for over the span of 5 years.