SINGAPORE — The strength of China’s armed forces is 20 years behind the U.S. and although the military is developing new capabilities, it is not a threat to peace in Asia, the Chinese defense minister said Sunday. China’s military won’t be used aggressively against its neighbors, General Liang Guanglie said at an Asian security conference in Singapore. “I know many people tend to believe that with the growth of China’s economy, China will become a military threat,” Liang said.