ST. LOUIS -- Vandals have targeted monuments dedicated to the leaders and soldiers of the secessionist, pro-slavery South of the Civil War era, painting the slogan "Black lives matter" on Confederate memorials in a half-dozen states.

The graffiti reflects the racial tension of post-Ferguson America, more than a week after a white man was accused of shooting and killing nine black congregants at a Charleston, South Carolina, church.

Michael Allen, a lecturer in American culture studies at Washington University in St. Louis, compared the vandalism to the toppling of statues in Russia at the end of the Soviet empire.

"If the monuments are strong statements of past values, defacing them is the easiest and loudest way to rebuke those statements," Allen said.

Confederate symbols, including the rebel battle flag, have been the subject of resentment for years. The anger boiled over after last week's massacre at the Emanuel African Methodist Episcopal Church. The suspect, Dylann Roof, had posed in online photos with the Confederate flag.

Politicians throughout the South are taking steps to remove the flag from public places. Black activists say the monuments should meet the same fate.

Racial wounds in the U.S. were torn open last August, when a white police officer in the St. Louis suburb of Ferguson, Missouri, fatally shot 18-year-old Michael Brown, who was black and unarmed. Officer Darren Wilson was cleared of any wrongdoing. "Black lives matter" has become a rallying call in protests that followed police violence against black men in other cities.

One of the defaced monuments was the Confederate Memorial in St. Louis' Forest Park, near Ferguson. The same graffiti was reported on memorials in Charleston; Baltimore; Austin, Texas; Asheville, North Carolina; and Richmond, Virginia. No arrests have been made.

With the Charleston shooting refocusing attention on Confederate symbolism, experts said, it isn't surprising that some people would take out their anger on monuments to those who fought on the side of slavery.

Elizabeth Brondolo, a psychology professor at St. John's University in New York who studies the effects of race on mental and physical health, said the defacing of memorials reflects a "consensus that there's been a very serious failure of empathy, a failure to understand what these symbols might mean to people who suffered from slavery and ongoing aggression."

The future of the 101-year-old statue in St. Louis was already in doubt. In April, Mayor Francis Slay ordered a study of what to do with it. Options include removing it.

Efforts have also begun to seek removal of Confederate monuments in Nashville, Tennessee; Shreveport, Louisiana; Orlando, Florida; Portsmouth, Virginia; and Birmingham, Alabama.