 During the 1820s , Duyệt 's continued cultivated of relations with the immigrant Chinese community that had settled in southern Vietnam in large numbers brought him into conflict with Minh Mạng . The general had adopted a Chinese immigrant merchant as his son and gave him favours , including appointing him to position of the body that regulated trade . The Japanese historian <unk> concluded that Duyệt and his entourage were given financial rewards and gifts from the Chinese merchants in return for favourable treatment by government officials . It was also pointed out that another of Duyet 's men was himself a businessman who had a Chinese agent . At the time , southern Vietnam was producing rice in plentiful quantities but export was banned by Minh Mạng , but prices in Vietnam , which were lower than those overseas , kept rising by 50 – 100 % in various parts of the country in five years . In the meantime , the opium supply kept on increasing . It was thought that Chinese merchants , whom Duyệt patronised , were illegally exporting rice at higher prices , and then bringing back opium during return journeys along with incoming immigrants . For his part , the general disagreed with the prevailing view held by the emperor , and said that people of both races were engaging in illegal trading , as well as blaming the incoming immigrants ' personal addictions rather than the Chinese merchants for bringing in opium . The historian Nola Cooke said that Duyet 's viewpoint was more plausible and speculated that the emperor 's stance was borne more out of a fear of the consequences of a disproportionate Chinese influence on the country than the reality of illegal trading . Duyệt wanted to further give tax concessions to newly arrived Chinese immigrants that were deemed to be impoverished to encourage immigration and speed up development of the region , something that the emperor was sceptical of , on the reasoning that it was difficult to genuinely determine who was in need and that the concession system was therefore open to <unk> . Nevertheless , Duyệt disobeyed Minh Mạng and tax concessions were granted . Because of their involvement in the illegal exportation of rice and importation of opium , Minh Mạng tried to ban the Chinese from engaging in sea trade in 1827 , but this was easily circumvented by the merchants , who exploited their contacts with Duyệt and used fraudulent registrations , often under the name of Vietnamese wives . It was not until Duyệt died that Minh Mạng was able to crack down on fraudulent sea trade . 
