Elementary students across America are taught that slavery ended in the 19th Century. But, sadly, nearly 150 years later, the fight to end this global scourge is far from over.
Today it takes a different form and we call it by a different name - "human trafficking" - but it is still an affront to basic human dignity in the United States and around the world.
The estimates vary widely, but it is likely that somewhere between 12 million and 27 million human beings are suffering in bondage around the world.
Men, women and children are trapped in prostitution or labour in fields and factories under brutal bosses who threaten them with violence or jail if they try to escape.
Earlier this year, six "recruiters" were indicted in Hawaii in the largest human trafficking case ever charged in US history.
They coerced 400 Thai workers into farm labour by confiscating their passports and threatening to have them deported.
I have seen firsthand the suffering that human trafficking causes. Not only does it result in injury and abuse—it also takes away its victims' power to control their own destinies. In Thailand I have met teenage girls who had been prostituted as young children and were dying of AIDS.
In Eastern Europe I have met mothers who lost sons and daughters to trafficking and had nowhere to turn for help.
This is a violation of our fundamental belief that all people everywhere deserve to live free, work with dignity, and pursue their dreams.
For decades, the problem went largely unnoticed. But 10 years ago this week, President Clinton signed the Trafficking Victims' Protection Act, which gave us more tools to bring traffickers to justice and to provide victims with legal services and other support.
Today, police officers, activists, and governments are coordinating their efforts more effectively.
Thousands of victims have been liberated around the world and many remain in America with legal status and work permits. Some have even become U.S. citizens and taken up the cause of preventing traffickers from destroying more lives.
This modern anti-trafficking movement is not limited to the United States. Almost 150 countries have joined the United Nations' Trafficking Protocol to protect victims and promote cooperation among countries.
More than 116 countries have outlawed human trafficking, and the number of victims identified and traffickers imprisoned is increasing each year.
But we still have a long way to go. Every year, the State Department produces a report on human trafficking in 177 countries, now including the US.
The most recent report found that 19 countries have curtailed their anti-trafficking efforts, and 13 countries fail to meet the minimum standards for eliminating trafficking and are not trying to improve.
It is especially important for governments to protect the most vulnerable – women and children – who are more likely to be victims of trafficking.
They are not just the targets of sex traffickers, but also labour traffickers, and they make up a majority of those trapped in forced labour: picking cotton, mining rare earth minerals, dancing in nightclubs.
The numbers may keep growing, as the global economic crisis has exposed even more women to unscrupulous recruiters.
We need to redouble our efforts to fight modern slavery. I hope that the countries that have not yet acceded to the UN Trafficking Protocol will do so.
Many other countries can still do more to strengthen their anti-trafficking laws. And all governments can devote more resources to finding victims and punishing human traffickers.
Citizens can help too, by advocating for laws that ban all forms of exploitation and give victims the support they need to recover.
They can also volunteer at a local shelter and encourage companies to root out forced labour throughout their supply chains by visiting www.chainstorereaction.com.
The problem of modern trafficking may be entrenched, but it is solvable. By using every tool at our disposal to put pressure on traffickers, we can set ourselves on a course to eradicate modern slavery.
Hillary Clinton is the US Secretary of State.