Today the Church remembers St. Andrew Dung Lac and the Vietnamese Martyrs. The following comes from American Catholic:
St. Andrew was one of 117 martyrs who met death in Vietnam between 1820 and 1862. Members of this group were beatified on four different occasions between 1900 and 1951. Now all have been canonized by Pope John Paul II.
Christianity came to Vietnam (then three separate kingdoms) through the Portuguese. Jesuits opened the first permanent mission at Da Nang in 1615. They ministered to Japanese Catholics who had been driven from Japan.
The king of one of the kingdoms banned all foreign missionaries and tried to make all Vietnamese apostatize by trampling on a crucifix. Like the priest-holes in Ireland during English persecution, many hiding places were offered in homes of the faithful.
Severe persecutions were again launched three times in the 19th century. During the six decades after 1820, between 100,000 and 300,000 Catholics were killed or subjected to great hardship. Foreign missionaries martyred in the first wave included priests of the Paris Mission Society, and Spanish Dominican priests and tertiaries.
Persecution broke out again in 1847 when the emperor suspected foreign missionaries and Vietnamese Christians of sympathizing with the rebellion of one of his sons.
The last of the martyrs were 17 laypersons, one of them a 9-year-old, executed in 1862. That year a treaty with France guaranteed religious freedom to Catholics, but it did not stop all persecution.
By 1954 there were over a million and a half Catholics—about seven percent of the population—in the north. Buddhists represented about 60 percent. Persistent persecution forced some 670,000 Catholics to abandon lands, homes and possessions and flee to the south. In 1964, there were still 833,000 Catholics in the north, but many were in prison. In the south, Catholics were enjoying the first decade of religious freedom in centuries, their numbers swelled by refugees.
During the Vietnamese war, Catholics again suffered in the north, and again moved to the south in great numbers. Now the whole country is under Communist rule.