American poet and writer Walt Whitman was born on May 31, 1819. Deeply touched by a visit to a wartime hospital, Whitman spent much of the Civil War as a hospital volunteer, carefully documenting his experiences caring for the wounded.

Officially titled "An Act to Organize the Territories of Nebraska and Kansas," this act repealed the Missouri Compromise, which had outlawed slavery above the 36° 30’ latitude in the Louisiana territories and reopened the national struggle over slavery in the western territories.

Drafted by James Madison, and presented by Edmund Randolph to the Constitutional Convention on May 29, 1787, the Virginia Plan proposed the foundation of what would become the U.S. Constitution: a strong central government composed of three branches: legislative, executive, and judicial.

Traditionally observed on the last Monday in May, Memorial Day was officially established by John A. "Black Jack" Logan, a charismatic Civil War general, Congressman, Senator, and commander of the Grand Army of the Republic in 1868, for "the purpose of strewing with flowers, or otherwise decorating the graves of comrades who died in defense of their country…" In this photo a Coast Guardsman observes a moment of silence before the graves of his fallen comrades on an unnamed atoll in the Pacific.

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The Mexican Punitive Expedition began in March of 1916, when General John J. Pershing led several thousand U.S. troops across the border into Mexico, following attacks on American citizens and property by the followers of Francisco (Pancho) Villa. Pershing’s orders from the War Department were to pursue and disperse Villa and his band or bands. Taken on May 27, 1916 by Tucker Beckett, this night-time photo shows members of the 16th Infantry around a campfire.

Dorothea Lange, whose photographs of the unemployed and migratory farm workers became synonymous with the Great Depression, was born on May 26, 1895. The caption of this photo reads "On Arizona Highway 87, south of Chandler. Maricopa County, Arizona. Children in a democracy. A migratory family living in a trailer in an open field. No sanitation, no water. They came from Amarillo, Texas. Pulled bolls near Amarillo, picked cotton near Roswell, New Mexico, and in Arizona. Plan to return to Amarillo at close of cotton picking season for work on WPA."

The photo is one of a series taken for an agricultural "Community Stability and Instability" study by the Bureau of Agricultural Economics. Taken by Dorothea Lange and Irving Rusinow, the photographs are a record of pre-World War II rural life and social institutions. Of particular interests are images of African Americans in Alabama and Georgia and migrant laborers hired to work in cotton fields in Arizona and California.