 The gold and slaves constituted an important source of income which could be used to finance the war, and therefore expeditions to Guinea became a priority for both belligerent sides.Portuguese ships had transversed the Andalusian coast, apprehending fishing and merchant ships, since the start of the war.To stop this, Isabella and Ferdinand sent four galleys under the command of Álvaro de la Nava, who stopped the Portuguese incursions and plundered the Portuguese city of Alcoutim on the Guadiana River.