Spain as we understand it now only really comes into existence in 1472 with the marriage of Ferdinand of Aragon and Isabelle of Castille, and the union of those two kingdoms.

The kingdom of Aragon under Ferdinand not only controlled the mediterranean coast of the Iberian peninsula, but also ruled over the islands of Sicily, Corsica and Sardinia. Therefore, the kings of Aragon and subsequent Spanish monarchs had strong interest in Mediterranean affairs throughout the late 15th century and early 16th.

This influence only increased when the kingdoms were united, making a more powerful Spanish kingdom. Beginning in 1501, Ferdinand waged a successful war against Louis XII for control of the kingdom of Naples. However, Ferdinand II formally took control of Naples as a possession of the crown of Aragon.

At this time, the Hafsid rulers of Tunisia were becoming more and more alarmed with increasing Aragonese influence in the Mediterranean. In 1509, a Spanish force took over the city of Oran on the coast of Algeria. In 1517, an army marched from Oran east to try and take the city of Tlemcen.

Concurrently, the Ottoman empire was expanding its influence in the eastern Mediterranean, conquering the Mamluk sultanate of Egypt in 1517. After this success, the eyes of the Sublime Porte looked to incorporate the North African coast into the Ottoman Realm.

Into this mix walked the brothers Khayr ad-Din and Aruj, who is better known as Barbarossa^1. Both were Aegean muslim privateers who had previous dealings defending the citizens of Tunis and Tlemcen against the Aragonese threat. In 1519, the Sultan Selim I would appoint Khayr ad-Din to lead his Jannisary forces in bringing that section of the North African coast under Ottoman protection, with the title of Governor as his reward.

From this position, Khayr ad-Din and Aruj would build up a Corsair fleet to threaten the security of Aragonese possessions. This threat would push Ferdinand's successor Charles I to dispatch an army to successfully capture Tunis in the 1535 as a part of Charles' larger war against the Ottoman sultan. In addition to being king of Spain, Charles was the leader of the Holy Roman Empire, and this era saw naval engagements throughout the Aegean and Mediterranean between Christian and Ottoman forces.

Spain would continue to control Tunis until 1574 when the Ottoman's recaptured the city for the last time.

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1- The name Barbarossa comes from the phrase Baba Aruj, meaning Father Aruj or Old Man Aruj. Interestingly, after Aruj was killed in battle with the Spanish, the name Barbarossa was passed on to his younger brother Khayr ad-Din, who would become known as Hayreddin Barbarossa by his christian opponents.

Empire of the Sea is a readable account of the ottoman-christian clash in the mediterranean in the middle decades of the 16th century. It gives some relevant information about Hayreddin Barbarossa and the 1535 capture of Tunis.