Horse 1848 - WW1: The War That Still Hasn't Ended

Mostly because I am a nerd, I love the minutiae of flotsam that means three-quarters of diddly squat to most people.
There was a byline in an article in the newspaper the other day about the totally koala unrine bonkers mental country that is North Korea and the fact that technically; because no peace treaty was signed and only an armistice of sorts was reached, the two Koreas are still at war with each other.

Now such states of diplomatic anomaly have existed before, such as the Third Punic War finally ending in 1985 after the mayors of modern Rome and Carthage signed a peace treaty and accompanying pact of friendship, or the Second World War only officially ending in 1990 with the Treaty on the Final Settlement with Respect to Germany after Germany had reunified; so I asked the question if any other cases of unfinished diplomacy have resulted in any other wars still technically persisting.
I found one. It is World War One.

On the 27th of January 1917, General Federico Tinoco Granados and his brother José Joaquín seized power and control the government in a military coup d'etat. Costa Rica would descend into its own well of instability and intrigue and so when the Armistice was finally reached, Costa Rica was too busy worrying about its own internal affairs (which amounted to martial law and a military dictatorship) to bother.
Federico declared war on the German Empire in May of 1918.

When the Treaty of Paris was finally signed, questions of legitimacy of Granados' government were far more pressing and so Costa Rica as a nation, never actually signed or agreed to the peace treaty. José Joaquín was assassinated in the first week of August of 1919 and on the 13th of August, Federico Tinoco resigned in favour of a series of Presidents who ran through the office as though it were a revolving door (that is he resigned because his government was unstable, not necessarily because there were a lot of would be presidents waiting to take office).

As Costa Rica was more concerned with establishing its own normalcy and never formally ended its state of war with Germany, technically that state of war still exists and World War One is still continuing more than 100 years after it started. It still has another 2149 years to go if it wants to beat the Punic Wars for the title of most protracted war in history though.