According to this US article from ABC News, thousands of people who were adopted by Americans aren’t necessarily US citizens because “Adoption for decades did not automatically make children citizens”.

Estimates range from 15,000 to 75,000 people who are might be affected and although many were adopted from South Korea, others were brought in from at least 24 other countries including Ethiopia and Romania.

2 of those adoptees have started the Adoptee Rights Campaign. The Campaign has heard from others

“… who’d been deported, some still living in hiding, others freshly discovering they’d never been made citizens. There is no government mechanism for alerting them. They find out by accident, when applying for passports or government benefits. One woman learned as a senior citizen, when she was denied the Social Security she’d paid into all her life.”

https://abcnews.go.com/US/wireStory/us-doesnt-american-thousands-adoptees-live-limbo-citizenship-115130078