Complex sentence: The current province of Sukhothai was at first known as Sawankhalok; it was renamed to Sukhothai in 1939 (which is why the railway system goes to Sawankhalok city and not Sukhothai city).
Split into simpler sentences: The current province of Sukhothai was at first known as Sawankhalok. It was renamed Sukhothai in 1939 (which is why the railway system goes to Sawankhalok city and not Sukhothai city).