Complex sentence: Tunis had initially been conquered by the Ottomans under Hayreddin Barbarossa in 1534, but the Holy Roman Emperor Charles V captured it in the Conquest of Tunis in 1535.
Split into simpler sentences: Tunis had initially been conquered by the Ottomans under Hayreddin Barbarossa in the Conquest of Tunis (1534). However, but the Holy Roman Emperor Charles V had recaptured it in the Conquest of Tunis in 1535.