'13th' wasn't around to watch in your history class. 13 reasons to watch it now.

If you see only one Oscar-nominated film this year, make it "13th."

Directed by Ava DuVernay, the stirring documentary explores America's long history of overpolicing and imprisoning black and brown people since the passing of the 13th Amendment. DuVernay sat down with scholars, educators, elected leaders, authors, and activists to tell this troubling but necessary story.

While these issues are difficult, we need to talk about them and, better yet, do something about them. "13th" truly couldn't have come at a better time.

Here are 13 lessons everyone should learn from this from powerful must-see film.

1. The 13th Amendment had so much promise ... almost.

Section 1 of the 13th Amendment reads:

"Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction."

The clause, "except as a punishment for crime whereof the party shall have been duly convicted," was included so farmers and landowners could essentially continue a form of slavery to support their businesses — so long as the black men and women were deemed criminals. There's no such thing as a throwaway clause in the Constitution. This is an intentional legal loophole.

2. The legal loophole in the 13th Amendment led to mass arrests and incarceration during the late 19th century.

It was the United States' first prison boom.

Black people were arrested en masse for petty crimes, like loitering or vagrancy, and incarcerated. Once labeled criminals, landowners and farmers could "lease" convicts from the state in exchange for full control of their lives.

3. While black men filled prisons, popular culture stoked fears.

Black men were portrayed in films as menacing, evil, and in relentless pursuit of white women.

In the 1915 film, "Birth of a Nation," which is essentially three hours of racist propaganda masking as a historical film, a white woman throws herself off a rocky cliff to save herself from being assaulted by a black man. Critics raved, drowning out mounting protests.

As a result of the popular film, membership in the Ku Klux Klan boomed.

4. As the KKK grew, black people were terrorized and murdered.

Lynchings were used to reinforce white supremacy while traumatizing and terrorizing black people. There was a disgusting entertainment aspect to it, as mobs of white people — including elected officials and community leaders — gathered to watch victims get beaten, shot, and tortured. Picture postcards were made of the swinging, mutilated bodies.

More than 4,000 lynchings occurred between 1877 and 1950 across Texas and the American South.

5. The murder of Emmett Till kickstarted the Civil Rights movement.

14-year-old Emmett Till was brutally beaten and murdered by a group of white men for allegedly whistling at and flirting with a white woman in 1955. (The woman recently admitted she fabricated at least part of her testimony.) Photos from his open casket funeral and the face of Till's weeping mother sent shockwaves around the country, galvanizing black people and their allies in the fight for equality.

6. But then the War on Drugs started an unrelenting wave of mass incarceration.

Crime started to increase in the early 1960s, and many in power quickly blamed the uptick on the end of segregation. Before long, the word "crime" was a stand-in for the word "race."

Nixon appealed to southern Democrats with thinly-veiled racism and promises to clean up the streets. His rhetorical "War on Drugs" became very real in the 1980s under President Reagan, who threw money, resources, and the full weight of the executive branch behind the issue. A wide swath of an entire generation was essentially removed from the narrative.

7. The numbers are astonishing. Full stop.

In 1970, there were 196,429 sentenced prisoners in state and federal prisons. In 1980, there were 329,821 people in state and federal prisons, and by 1990, that number more than doubled to 771,243.

Today, the American criminal justice system holds 2.3 million people. This is not normal. It is not OK.

8. Republicans are not solely to blame for this crisis. President Clinton did his part too.

In the wake of President Reagan and President George H.W. Bush, appearing "soft on crime" wasn't an option for President Bill Clinton. In 1994, he signed the Violent Crime Control and Law Enforcement Act. It expanded the list of death penalty eligible offenses and included a "three strikes" provision, which meant mandatory life sentences for people convicted of their third felony. It also funded new prisons and provided the budget for 100,000 police officers.

9. Sadly, there's a lot of money to be made off mass incarceration.

Private correctional facilities made a reported $629 million in profits in 2014, and that's just scratching the surface. From the corporations building and maintaining prison facilities, to the food vendors, health care providers, and equipment and textile manufacturers who keep them running, many companies have a lot to gain from maintaining the status quo.

10. As mass incarceration starts to get a bad rap, the winds are shifting — and not necessarily for the better.

As mass incarceration and America's prison problem take center stage, legislators and businesses are looking for new ways to redefine the narrative while still making money. What does that look like? For starters, monetizing bail, probation, parole, and house arrest.

11. We can't forget the people and families caught in the struggle.

In 2010, 16-year-old Kalief Browder was arrested for a robbery he insisted he did not commit. Browder was thrown into an adult correctional facility where he would spend nearly three years awaiting trial and almost two years in solitary confinement. In 2013, the district attorney dismissed the case against Browder, and he went home a free — but forever changed — young man.

After many attempts, Browder died by suicide in May 2015.

Browder's story is far too common. Many poor people, especially poor people of color, are locked up for years either awaiting trial or because they cannot afford bail.

12. American prisons are intended to punish, but former felons continue to suffer after they have served their time.

Former felons are stripped of voting rights, have difficulty securing employment, applying for aid, and finding housing.

"Ban the box" campaigns that seek to end asking about felony convictions on job and aid applications are popping up across the country, and for many, these initiatives can't come soon enough.

13. As President Trump settles into office, many are worried about his next moves — and rightfully so.

He repeatedly refers to parts of Chicago as lawless, dangerous, and worse than parts of the war-torn Middle East. He's threatened the city with federal intervention to get the "carnage" under control. His repeated calls to arrest and deport undocumented immigrants tend to include gross mischaracterizations of immigrants as gang members, rapists, or drug dealers.

His "law and order" catchphrase is the same dog whistle Nixon used to kickstart the War on Drugs. His comments about Chicago and other inner cities are stoking fears and playing to the imaginations of his base, much like the horrifying scenes in "Birth of a Nation."

These facts are alarming, but here's what you can do about it.

Use your privilege for good. Pass the mic to voices that may go unheard. Help others register to vote. Support Ban the Box initiatives and organizations that help people with criminal records land on their feet.

Ask to see the numbers. Plenty of police data is publicly available. Check out the numbers in your community. Look at the demographics of people being stopped, arrested, or convicted. Numbers don't lie. Hold your leaders accountable and make them answer for racial disparities.

Stay active in schools. Overpolicing and the criminalization of black people doesn't begin and end with police officers. Black children are nearly four times as likely to be suspended as white children. Ask tough questions of your child's teachers and administrators. Attend school board meetings.

This is no ordinary crisis and it will require extraordinary solutions.

Watch the film, do your part. Let's get to work.