How long was the longest war in history?

The "Roman-Persian Wars", It began with the Roman conquest of Parthia in 92 BC and lasted until the final war of the Byzantium and the Sassanid Eran-Shahr in 627 AD. This series of conflicts which lasted more than 700 years became the longest war between two entities in all of history, until it eventually came to an end with the Arab Muslim conquests of the 7th century.

However, the longest SINGULAR war, and not series of wars, was the Hundred Years' War, officially lasting from 1337 (when war was declared) to 1475 (when the treaty was signed) and the majority of conflict lasting from 1328 (when the French King died leaving no sons, and the English King put forth his claim) to 1453 (when Bordeaux was recaptured by France, ending Europe's fighting). So the Hundred Years' War between the English and France lasted 138 years officially, or 125 years of actual conflict between the two nations.

Another View:

It is untenable to talk of a continuous war between Parthia and Rome for 700 years. A 'series of conflicts' is not a single 'War'. Warfare amongst the aboriginal people in Australia lasted about 60,000 years but we would hardly call it 'a war'.

A sensible answer to the question would be to look at the Hundred Years War between England and France 1337-1453 CE.