For nearly 2 centuries, Denmark was at war with the Spanish town of Huéscar – but not a single shot was fired, and no one was killed. After war was declared in 1809, everyone completely forgot about it, so there were never any battles. A peace treaty was finally signed in 1981, when a historian happened upon the official declaration of war and realized the countries technically should have been fighting each other for the past 172 years. Source Source 2 Source 3