The causes of anti-Western sentiment in China include the collective memory of the period of Chinese history beginning with the two Opium Wars between 18391860 and ending with the expulsion of the Japanese after the Second World War which is known to the Chinese as the century of humiliation when China was sacked by a western coalition. Wang Zheng wrote that it was "attacked, bullied, and torn asunder by imperialists". Kenneth Lieberthal, a political science professor at the University of Michigan, has argued that the demonstrations in Western cities during the Olympic torch relay had "deep historical resonance" amongst Chinese, who suspect that after China's recovery from its fall in international stature from 150 years ago, "the West is trying to humiliate them again". Supporting this view, a 2007 survey found that 45% of the Chinese general public believed that the U.S. was "trying to prevent China from becoming a great power" compared to 32% who believed that the U.S. accepted "China's status as a rising power", 23% were "not sure". Although this sentiment has been partially assuaged by the return to China of Hong Kong and of Macau, the unresolved political status of Taiwan remains for some a reminder of China's weakness and division.