Andrew (Unam Sanctam) has a superb illustrated post about the Vietnamese martyrs who underwent some of the worst tortures in the history of Christian martyrdom - which is saying something. As well as torture, there was forced indignity. From 1832 Minh-Mang excluded all foreign missionaries and ordered Vietnamese Christians to renounce Christianity by trampling on the crucifix.
There is a single feast day for all the Vietnamese Martyrs - 117 were particularly named by Pope John Paul II but there were in excess of 130,000 who gave their lives for the faith from 1516 to the 20th century. 8000 Vietnamese in exile participated in the canonisation on 9 June 1988 as representatives for their catholic countrymen in Vietnam, who not were allowed to leave the country.
As is shown in the evangelisation of so many countries, including our own, the Christian missionaries brought many benefits. For example, the system of writing Vietnamese, called Quốc Ngữ or "national language" which is still used today was perfected in the 17th century by Alexandre De Rhodes, a Jesuit missionary.
Do see Andrew's full post for lots more.