His fear of Ren making legendary weapons in other countries is fking scary as the leaders of the nation after all.
If the author is taking examples from actual real-life history where in a number of cases, certain individuals were too valuable and dangerous for a country to allow to move to another country. If that person moved there, they would either create economic competition due to their knowledge of inventions, or they could be too effective in plotting the downfall of the country they came from. In these cases, they were imprisoned to work for that kingdom/empire or they were executed.
