The event you are referring to is likely the "Bonus Army" march, which took place in Washington, D.C., in 1932 rather than a specific incident labeled as a "Massacre." In this event, World War I veterans, known as the Bonus Army, organized to demand early payment of bonuses that had been promised to them for their service. They set up camp in the city, leading to tensions with police and the government.
The situation escalated when the government, led by President Herbert Hoover, ordered the police to disperse the marchers. On July 28, 1932, clashes broke out between the veterans, police, and ultimately the U.S. Army, which was called in to clear the camps. The confrontation resulted in violence, with several veterans killed and many others injured.
This incident highlighted the desperation of many veterans during the Great Depression and raised public awareness and sympathy for their plight. It was a pivotal moment in U.S. history, demonstrating the government's response to civil unrest and the struggles faced by returning soldiers. If you were referring to another specific "Massacre" or incident, please provide more details, and I'd be happy to elaborate!