Final answer:
Roman Polanski, the director of 'Chinatown', fled the United States in 1978 to escape sentencing for unlawful sexual intercourse with a minor.
Step-by-step explanation:
The Oscar-nominated director of Chinatown who fled the United States in the '70s is Roman Polanski. Polanski left the country in 1978 after pleading guilty to unlawful sexual intercourse with a minor. His decision to flee was made in order to avoid sentencing after a complex and controversial legal battle that continues to influence his career and legacy.