Original: With the Reconquista in full swing after the conquest of Cordoba in 1236, the Moorish Nasrid dynasty aligned themselves with Ferdinand III of Castile, officially becoming a tributary state in 1238. The state officially became the Kingdom of Granada in 1238.
Simplified: As the Reconquista was very successful after the conquest of Cordoba in 1236, the emirate officially became a tributary state in 1238 and was called the Kingdom of Granada.