Buying second passports was once largely the preserve of the superrich, but one investment migration firm says that’s changing as more middle-class Americans shop for them.

The investment migration industry has traditionally catered to those who can afford the six or seven-figure price tags of many “golden visas.” Peter Thiel, who was granted New Zealand citizenship in 2011 and temporarily relocated to Argentina this year, is among the billionaires to seek additional passports and residences.

For wealthy Americans, acquiring another citizenship generally doesn’t eliminate their US tax obligations, but offers the freedom to live, travel, and…