Although this isn't quite confirmed, it is considered that Germanic wars are the longest-lasting wars in history. They lasted for 800 years, starting from 220 BCE until 580 AD, and were fought between Romans and various Germanic tribes. However, if you need a war in the newer history, the second longest war is known as Reconquista, which is a war fought between Christian Kingdoms and the Muslim Moors, and lasted for about 770 years.
