Sauron's spirit also escaped, and fled back to Middle-earth, where he again raised mighty armies to challenge Gondor and Arnor. With the aid of Gil-galad and the Elves, Sauron was defeated, and the Third Age began. Sauron vanished into the East for many centuries, and Gondor and Arnor prospered. As Sauron re-formed and gathered strength, a series of deadly plagues came from the East. These struck harder in the North than the South, causing a population decline in Arnor. Arnor fractured into three kingdoms. The chief of the Nine Ringwraiths, the Witch-king of Angmar, assaulted and destroyed the divided Northern Dúnedain kingdoms from his mountain stronghold of Carn Dûm. After their fall, a remnant of the northern Dúnedain became the Rangers of the North, doing what they could to keep the peace in the near-empty lands of their Fathers. The surviving Dúnedain of Arnor retreated to the Angle south of Rivendell, while smaller populations settled in far western Eriador. The fragmentation of the kingdoms has been compared to that of the early Frankish kingdoms.