A photograph of a runaway slave named Gordon was taken in 1863 in Louisiana, where he was being treated by medical staff prior to enlisting in a Yankee regiment of Colored Troops during the Civil War.

An engraving of the photo, showing Gordon's back severely-scarred from repeated whippings, was featured in the July 4, 1863 issue of Harper's Weekly, and reproductions were used by abolitionists in their cause to rid America of the scourge of slavery.

While serving with the Union Army, Gordon was at one point taken prisoner by rebel forces, beaten and left for dead, but he managed to escape and rejoin the Union side.

Founded by Luis Valdez in 1965 as a cultural arm of the United Farm Workers of America, the Teatro Campesino energized the union's political message using song, music and drama.

Though in its early years the group raised funds for striking workers, Teatro Campesino would later explore Chicano culture beyond the issue of labor. Valdez himself would create the musical stage show "Zoot Suit" and direct the film "La Bamba."

As founder and president of the United Farm Workers, Cesar Chavez (1927-1993) brought the plight of migrant farm laborers to national consciousness.

The boxing gloves of Cassius Clay/Muhammad Ali, who through his skills in the ring and the controversy he generated outside the ring (including fighting the U.S. military draft on conscientious objector and religious grounds) became one of the most famous figures of the 20^th century.

Inspired by the 1963 March on Washington, gay rights activist Frank Kameny (1925-2011) organized three protests outside the White House in 1965, calling for civil rights for the LGBTQ community.

Left: Three handmade signs used during Kameny's protests.

In the early 1960s, disability-rights pioneer Ed Roberts (1939-1995), who had contracted polio as a teenager, led efforts to establish a program for disabled students at the University of California, Berkeley.

Roberts later founded the Independent Living Movement, a worldwide campaign to secure civil rights, equal access, and self-sufficiency for people with disabilities.

Since the 1920s a proposed Constitutional Amendment to protect against sexual discrimination of woman had been met with failure, until 1972, when it was passed in the House and Senate. Activists opposed to the Equal Rights Amendment (including religious conservatives and the Eagle Forum's Phyllis Schlafly) fought its adoption by the minimum 38 state legislatures required for ratification. The measure died.

Left: A "Stop ERA" button, c. 1978.

For more info:

Smithsonian: National Museum of American History

Smithsonian: National Museum of African American History and Culture

Smithsonian: National Portrait Gallery

"The Smithsonian’s History of America in 101 Objects" by Richard Kurin (Penguin)

By CBSNews.com senior producer David Morgan