The United States and the Eastern Alliance (Russia, China, etc.) are in a cold war, racing to be the first to set up a military base on the moon. One day, a statistician notices that an alarmingly high fraction of the previous day's births in New York City were girls. Soon, it becomes clear: no male children have been conceived in the past nine months or so, worldwide. This is a pandemic worth suspending the arms race to solve.
Despite the best efforts of the world's scientist's, and the American and Russian supercomputers, no solution is found. As a desperate, last-ditch effort, the Americans and Russians send two people to the moon--an American man and a Russian woman--to see if a male child can be conceived away from the Earth.
Upon returning, the astronauts report that they were kidnapped by aliens, and only just managed to escape in time to return to Earth. Whatever ray was causing the lack of male conceptions seems to have been shut off, presumably because the aliens have left to retrieve reinforcements. So Russia and America renew their determination to work together in the face of this new threat.
It turns out that the two astronauts had been hypnotized by the supercomputers, and there were no aliens at all. The lack of male births was caused--and ended--by the computers in order to avert a devastating war.