In 1578, the Castilian War erupted between the Christian Spaniards and Muslim Bruneians over control of the Philippine archipelago. On one side, the newly Christianized Non-Muslim Visayans of the Kedatuan of Madja-as and Rajahnate of Cebu, plus the Rajahnate of Butuan (which were from northern Mindanao), as well as the remnants of the Kedatuan of Dapitan had previously waged war against the Sultanate of Sulu, Sultanate of Maguindanao and Kingdom of Maynila, then joined the Spanish in the war against the Bruneian Empire and its allies, the Bruneian puppet-state of Maynila, Sulu which had dynastic links with Brunei as well as Maguindanao which was an ally of Sulu. The Spanish and its Visayan allies assaulted Brunei and seized its capital, Kota Batu. This was achieved as a result in part of the assistance rendered to them by two noblemen, Pengiran Seri Lela and Pengiran Seri Ratna. The former had traveled to Manila to offer Brunei as a tributary of Spain for help to recover the throne usurped by his brother, Saiful Rijal. The Spanish agreed that if they succeeded in conquering Brunei, Pengiran Seri Lela would indeed become the Sultan, while Pengiran Seri Ratna would be the new Bendahara. In March 1578, the Spanish fleet, led by De Sande himself, acting as Capitán General, started their journey towards Brunei. The expedition consisted of 400 Spaniards and Mexicans, 1,500 Filipino natives and 300 Borneans. The campaign was one of many, which also included action in Mindanao and Sulu.