On July 30, 1866, during the turbulent Reconstruction era after the Civil War, white resistance to African American citizenship turns violent in New Orleans when a white mob kills dozens of African Americans gathering to support a political meeting.

The New Orleans Massacre, also called the New Orleans Riot, happened at the New Orleans Mechanics Institute, where 25 state delegates were reconvening the 1864 Louisiana Constitutional Convention. The state’s new constitution already had abolished slavery, but the state legislature passed laws limiting the rights of people freed from slavery. The Radical Republicans wanted to redo the constitution so that freedmen would gain voting rights. Another aim was to eliminate the Black Codes and disenfranchise former Confederates.

Two of New Orleans’ main leaders—Mayor John T. Monroe, a Confederate sympathizer, and Sheriff Harry T. Hays, a former Confederate general—strongly opposed the new constitutional convention. After a political rally on July 27, Hays gathered a posse of white officers, mostly ex-Confederates, to disrupt the convention, which began at noon on July 30.

As the delegates filed into the building, a crowd of protesters gathered outside the Mechanics Institute. Meanwhile, about 200 unarmed Black people, mostly Union veterans, approached the building in a parade form to show support. As they approached the building, bystanders harassed the marchers and isolated scuffles broke out.

When Hays and his men arrived on the scene, things turned deadly. Officers fired into the crowd, and while some marchers fled into the Mechanics Institute, many others were massacred there on the street. Accounts of casualties vary, but a National Park Service article reports that 34 African Americans were killed and 119 were wounded; three of the white delegates were killed and 17 were wounded.

U.S. General Absalom Baird, whose role was maintaining order and suppressing violence in the region during Reconstruction, wired Secretary of War Edwin Stanton that afternoon with this report: “Immediately after this riot assumed a serious character, the police, aided by the citizens, became the assailants, and from the evidence I am forced to believe, exercised great brutality in making their arrests. Finally, they attacked Convention Hall and a protracted struggle ensued. The people inside the hall gave up some who surrendered, and were attacked afterward and brutally treated.”

General Philip Sheridan, reporting to the War Department, said that delegates and peaceful supporters got hit “with fire-arms, guns and knives, in a manner so unnecessary and atrocious as to compel me to say that it was murder.”

“It was no riot,” Sheridan said. “It was an absolute massacre by the police … without the shadow of a necessity.”

The tragedy in New Orleans and previously in Memphis—where a similar deadly riot happened in early May of 1866—led to major changes in the country’s Reconstruction policy. The Radical Republicans earned a majority in both the House of Representatives and the Senate in the mid-term election of 1866. This helped to pass the 14th and 15th Amendments, which guaranteed citizenship to all people born or naturalized in the U.S.—including those freed from slavery—and gave African American men the right to vote.