Complex sentence: This movie was based on the short story "Liang Ge Youqijiang" written by Huang Chunming; it was uncredited because Huang's works were banned in South Korea at the time.
Split into simpler sentences: This movie was actually based on an uncredited short story "Liang Ge Youqijiang" written by Huang Chunming. The reason being that his works were banned in South Korea at the time.