"Legend has it that the brothers of the same surname from Water Margin eventually fled to Vietnam. Of course, they might have only spread their seeds, with the veracity of the legend unknown…
"After Vietnam became an independent country, it had the Lý and Trần dynasties. The Lý dynasty ruled for more than two hundred years. This made many of the old guards continue having their allegiance with the Lý dynasty while viewing the Trần dynasty with animosity even after the latter grew in power. To the ruler of the Trần dynasty, he believed that since these people like Lý that much, they should just all change their surname to Nguyen.
"Of course, that's just one story. As for the actual reason for the change in surnames, it's uncertain. Perhaps it was a spur of the moment decision by the Trần dynasty emperor or perhaps he had a screw loose, or maybe there was some other reason. In any case, the changing of surnames is a true historical event.