The UN Population Fund puts it well:

Child marriage is a human rights violation. Despite laws against it, the practice remains widespread, in part because of persistent poverty and gender inequality. In developing countries, one in every four girls is married before reaching age 18. One in nine is married under age 15.

Child marriage threatens girls’ lives and health, and it limits their future prospects. Girls pressed into child marriage often become pregnant while still adolescents, increasing the risk of complications in pregnancy or childbirth. These complications are a leading cause of death among older adolescents in developing countries.

UNICEF is even more forceful:

Marriage before the age of 18 is a fundamental violation of human rights. Many factors interact to place a girl at risk of marriage, including poverty, the perception that marriage will provide ‘protection’, family honour, social norms, customary or religious laws that condone the practice, an inadequate legislative framework and the state of a country’s civil registration system. Child marriage often compromises a girl’s development by resulting in early pregnancy and social isolation, interrupting her schooling, limiting her opportunities for career and vocational advancement and placing her at increased risk of domestic violence. Child marriage also affects boys, but to a lesser degree than girls.

These children are insufficiently developed to vote or drive under the law, yet they can freely consent to a possibly life-long legal partnership? Ridiculous. It’s not hard to find stories of girls who felt like slaves to their husbands, or had to endure years of abuse before they could legally divorce. And the excuses given to protect it defy belief at times.

Last year, 17-year-old Girl Scout Cassandra Levesque campaigned to change the New Hampshire law that allows girls as young as 13 to get married if their parents approve. “My local representative introduced a bill that raised the minimum age to 18. But a couple of male representatives persuaded the others to kill the bill and to prevent it from being discussed again for some years,” she says. “One of them said that a 17-year-old Girl Scout couldn’t have a say in these matters.”

“So they think she’s old enough for marriage, but not old enough to talk about it,” says Reiss. “I think that reasoning is terrifying.”

My point exac-

… Wait. “New Hampshire?!”

In 2013, [Sherry] Johnson was working at a barbecue stand in Tallahassee when she told her story to a senator who was one of her regular customers. “She listened to me and decided to do something,” Johnson recalls. “She presented a bill to restrict child marriage in 2014, but it failed. That was because nobody understood the problem at the time. “People thought: this can’t happen in Florida. The minimum marriage age is 18; what’s the problem? But they didn’t know about the loopholes. Between 2001 and 2015, 16,000 children were married in Florida alone. A 40-year-old man can legally marry a five-year-old girl here.”

Child marriage is semi-legal in New Hampshire and Florida? That can’t be right.

In most US states, the minimum age for marriage is 18. However, in every state exceptions to this rule are possible, the most common being when parents approve and a judge gives their consent. In 25 states, there is no minimum marriage age when such an exception is made.

…. What the hell, USA? How could you allow over 200,000 children to get married between 2000 and 2015? How could your judges approve marriages before one party can even consent to sex?! Between this and your poor maternal health outcomes, your unsustainable military spending, your dysfunctional political system, and your growing reputation as a tax haven and money launderer, I have half a mind to invalidate your “developed country” card.

(Thanks to blf for pointing me to this outrage.)