The Japanese believed that Chang Hsüeh-liang, who was known as a womanizer and an opium addict, would be much more subject to Japanese influence than was his father. On this premise, an officer of the Japanese Kwantung Army therefore killed his father, Zhang Zuolin (the "Old Marshal"), by exploding a bomb above his train while it crossed under a railroad bridge. Surprisingly, the younger Chang proved to be more independent and skilled than anyone had expected. With the assistance of Australian journalist William Henry Donald, he overcame his opium addiction and declared his support for Chiang Kai-shek, leading to the reunification of China in 1928.