Twenty-seven million. That is the number of people experts estimate are currently enslaved around the world. I first heard that number during my junior year of high school, when I began reading in Nicholas Kristof’s The New York Times column about the atrocious human rights abuses perpetrated against those millions of slaves, a phenomenon also known as human trafficking.

But 27 million is not an easy number to conceptualize – how many is that, really? Twenty-seven million people would fill Kinnick Stadium for every home game for the next 50 seasons of college football. Twenty-seven million people are more than the combined populations of Iowa, Minnesota, Wisconsin, Nebraska, Missouri and Kansas.

I used to wonder how so many people could continue to be enslaved around the world without anyone noticing or raising the alarm. This summer, during my internship at the international anti-slavery organization Free the Slaves, I began to understand. Among other appalling traits, modern-day slavery is differentiated from historical slavery by how effectively it is hidden in plain view.

The U.S. State Department estimates this is a $32 billion industry worldwide, second in size and scope only to drug trafficking. In the United States, where the Emancipation Proclamation abolished slavery 150 years ago, it continues to thrive. In fact, between 15,000 and 17,500 people are trafficked into the United States annually, not to mention the thousands of United States citizens lured into trafficking situations every year.

These trafficking victims include men, women and children of all ages, classes, races and nationalities who are lured into the commercial sex industry, sweatshops, farm labor, domestic work, restaurants, hotels, construction work and other low-wage industries.

Even in Iowa, slavery continues to flourish. Over the past year, Iowa news stations and law enforcement have turned their attention to the countless cases of human trafficking in places like Davenport, Evansdale and Muscatine County. Young girls lured from their homes and families and forced into sexual slavery have been a particular focus of these investigations and news stories. However, as an agricultural state, Iowa must also be vigilant about human rights abuses that occur in the large-scale farming industry, where hundreds of undocumented immigrants are forced to work for little or no pay.

Hopefully, as public awareness increases, more people will join the fight again human trafficking and help victims and survivors get help. One step the United States has already taken is the passage of the Trafficking Victims Protection Act. However, Congress let the act expire in 2011 – depriving our country of its strongest tool for fighting modern-day slavery.