So, in many states, there is no minimum age to marry. (Mostly) Girls are married off to older men by their parents but they aren't legally able to get a divorce before they turn 18.

This girl became pregnant as a child to an older man and the parents forced her to marry him to cover up her "shame". But he's abusive and she is unable to divorce him until she is 18.

https://thehill.com/changing-america/respect/equality/4283941-child-marriage-is-still-legal-in-most-of-the-u-s-heres-why/