Aragon had been trying to subjugate Sardinia since the reign of James II, and gradually the Aragonese had conquered most of the island.
However, in the 1380s, in the reign of Martin's father Peter IV, the remaining independent principality of Arborea had become a fortress of rebellion and the Aragonese were rapidly driven back by Eleanor of Arborea, so that practically the whole of Sardinia had been lost.
William III, Viscount of Narbonne, is the grandson of Beatrice, youngest daughter of Marianus IV of Arborea and Timbra de Rocabertí, and Aimery VI of Narbonne (married 1363).
When Marianus V, the youngest son of Beatrice' elder sister Eleanor, died in 1407, Arborea had experienced a succession crisis.
The late Beatrice had a claim to the judgeship which was picked up by her grandson, the son of William II.
The de jure judge from 1407 is Leonardo Cubello, great nephew of Hugh II of Arborea.
King Martin of Aragon has sent his son Martin the Younger, King of Sicily, to reconquer Sardinia.
On October 6, 1408, Martin had disembarked at Cagliari with a strong army.
On December 8, William had also reached Cagliari, and is crowned "King of Arborea, Count of Goceano, and Viscount of Bas" at Oristano on January 13, 1409.
