What war lasted the longest?

The Iberian Religious War

Explanation: The war started about 718, and ended in 1492 It lasted for 781 years  more than three times as long as the United States has existed

tenochtitlan (also spelled tenochtitlán), located on an island near the western shore of lake texcoco in central mexico, was the capital city and religious centre of the aztec civilization. the traditional founding date of the city was 1345 ce and it remained the most important aztec centre until its destruction at the hands of the conquering spanish led by hernán cortés in 1521 ce, which led to the final collapse of the aztec empire.