The alliance between Achaea and Epirus is very unstable.

Michael of Epirus has meanwhile set his sights on Thessalonica.

Despite several efforts to reach a diplomatic settlement, the issue between the rival contenders has finally to be resolved in Macedonia on the plain of Pelagonia.

Manfred sends four hundred knights in support of the Epirote and Achaean forces, but the allied operation is compromised by mutual suspicion.

Michael's illegitimate son John Doukas deserts to the enemy and Michael himself abandons his allies while the Nicaeans, led by John Palaiologos, a brother of Emperor Michael VIII Palaiologos, inflicted a crushing defeat on William, who is captured in the battle.

Consequently, while Michael flees to the Ionian islands, …