Complex sentence: In 1542 de Soto's expedition encountered a powerful nation they called the "province of Quigualtam", an Emerald-phase precursor of the historically known Natchez chiefdom.
Split into simpler sentences: In 1542 de Soto's expedition encountered a powerful nation which they called the "province of Quigualtam". Scholars have classified this as an Emerald-phase precursor of the historic Natchez chiefdom.