IRVINE, Calif. — The knock came at night more than 30 years ago. Hugo Van, then a young man, had a chance to flee newly communist Vietnam and walk to freedom.

There were no guarantees, but Van didn’t hesitate to take the risk. With a few hundred dollars, he and his younger sister got a car ride to a Vietnamese village, then a boat to Cambodia and began the trek across barren land until they were caught by Cambodian soldiers. For nearly two weeks, they were held in a camp where they were given wormy rice to eat and Van found himself staring down the barrels of six guns as guards attempted to attack his younger sister.

“Everybody knew: boat or walk,” Van, now 57, told his American-born daughter in words she was hearing for the first time. “When you escape ... you use your life to bet.”...