Fifty years ago this month, an interracial group of activists decided to take a risky step and put their bodies on the line to challenge the entrenched policy of racial segregation in the American South. They came to be known as the Freedom Riders.

The group had federal law on its side, as a recent Supreme Court decision, Boynton v. Virginia, had deemed “white only” facilities in interstate bus terminals as illegal. But that did not matter to the racist mobs, some of them organized by local police officers, which descended upon the activists when they arrived in Alabama. These mobs bloodied the Freedom Riders in Birmingham and firebombed their bus in Anniston. Scores of activists were arrested when they got to Mississippi, where police threw them into the state’s famous Parchman prison.

The Freedom Riders knew the dangers they faced. Some female riders pinned names of the next of kin to their bra straps, so that in the event that they were killed, their families would be able to identify them.

A Northern civil rights organization, the Congress of Racial Equality, launched the Freedom Rides. Then, leaders of the newly formed Student Nonviolent Coordinating Committee organized more of them.

“Traveling in the segregated South for black people was humiliating,” said Diane Nash, one of the principal organizers. “The very fact that there were separate facilities was to say to black people and white people that blacks were so subhuman and so inferior that we could not even use public facilities that white people used.” White allies — like James Zwerg, whose bloodied and swollen face made headline news — risked their lives alongside black activists. However, the leadership of the rides came from black activists themselves.

The Freedom Rides were conceived both to strike a blow against white supremacy and to assert the humanity of black people. The Riders were ordinary people who overcame their fears to up the ante in the fight for racial justice. They embodied a collective spirit of determined resistance that can only be described as inspiring. When they were arrested and jailed, they were defiant, singing even as their captors threatened them.

Today, there is a new generation of activists who are keeping that spirit of resistance alive through their own campaigns. Like the Freedom Riders, they are challenging the ways in which citizenship and human rights are denied to certain sectors of the population.

One group is Critical Resistance, which focuses on the issue of mass incarceration and the prison industry’s insatiable hunger for young black and brown bodies. A new documentary film, “Visions of Abolition,” tells its important story.

Another group is the National Immigrant Youth Alliance, which is organizing undocumented young people in Detroit and Chicago and has gone down to Georgia to do the same. There, the group’s members have been embraced by veteran civil rights leaders.

On one level, these struggles are very different from one another, but in some fundamental ways they are part of the same tradition. It’s a tradition that has pushed against the narrow definitions of who can and cannot lay claim to citizenship — a tradition unafraid to confront the powers that be in pursuit of a more just society.

• Ransby is an associate professor in the department of African-American Studies and History at the University of Illinois at Chicago.