They *do* have those 30 million males that no doubt have large chips on their shoulders, and if they can’t have a Chinese woman, might as well go kill some enemies and take *their* women...
Imposing their birth control policies on the people of China has led to a disaster for China. I would not doubt they will have to start a war soon in order to keep the lid on the 30 million sexually frustrated males of China who are without, and will certainly remain without, women.