The waters of Quảng Yên belong to the Gulf of Tonkin, adjacent to the East Sea (also known as the South China Sea), and held an important position economically, militarily, and politically for the Đại Việt nation. International and Vietnamese historians have pointed out that, very early on, this place was home to an international trading port system, acting as a trade gateway between Đại Việt and northern countries such as Japan and China and southern countries such as Champa, Chenla, Thailand, the Philippines, and Indonesia. But by the Nguyễn Dynasty, the situation had changed a lot. In this article, we rely on documents from historical books such as Đại Nam thực lục (大南寔錄, - Chronicle of Đại Nam), Đại Nam nhất thống chí (大南一統志-Đại Nam Comprehensive Encyclopaedia), and Châu bản triều Nguyễn ( 阮朝硃本- Official Documents of Nguyễn Dynasty), to present some of the status and policies of King Minh Mạng in exploiting and protecting the waters of Quảng Yên.