Complex sentence: In 1244, he lost Arjona to Castile; in 1246 he agreed to surrender Jaén and accept Ferdinand's overlordship in exchange for a twenty-year peace.
Split into simpler sentences: In 1244, he lost Arjona to Castile. Two years later, in 1246, he agreed to surrender Jaén and accept Ferdinand's overlordship in exchange for a twenty-year peace.