Q. Which two nations military conflict is "Castilian War of 1578"?
Answer: Brunei and Spain
Notes: Spanish Expedition to Borneo, also known as the Castilian War, was a military conflict between Spain and Brunei in 1578. As part of the European competition to control southeast Asia, Spaniards arrived in Brunei during the mid-16th century. Apart from the trade interests, Spaniards have intentions to spread Christianity which was vociferously rejected by the then Muslim regime of Brunei which finally lead to a war in 1578.