CHARLESTON, S.C. - A Civil War commemoration focused on the Confederate side of the conflict, marking South Carolina's decision 150 years ago to secede, drew protesters with modern-day civil-rights concerns Monday.

Outside the Charlestown auditorium where the "Secession Ball" was held, whites and blacks demonstrated together as predominantly white ball participants - men in period evening dress and gloved women in flowing dresses - went in.

NAACP leaders said the gala honored men who committed treason for the sake of a system that kept black men and women in bondage. Some compared Confederate leaders to terrorists and Nazis.

"It's disgusting and unbelievable they would have a gala celebration to honor a day that ended up causing so much suffering," said Dot Scott, president of the Charleston branch of the National Association for the Advancement of Colored People.

Lonnie Randolph, head of its South Carolina chapter, likened the ball to celebrating the attack on Pearl Harbor.

Organizers of the $100-a-person event said it was not celebrating slavery but was a fund-raiser to honor men who sacrificed their lives for their vision of states' rights and to help pay for preserving Confederate-era archives.

"It's hard for us to judge the situation that existed then by today's standards. I think slavery is an abomination. But it's a part of history, legal at the time. I don't agree with it, but it was," said Randy Burbage, vice president of the Confederate Heritage Trust, which helped put on the ball.

"Any group that wants to call our ancestors terrorists and compare them to Nazi soldiers we will not negotiate with," he said.

John Genes 2d bought two of the 400 tickets sold for the event. His great-great-grandfather fought with a South Carolina regiment in the war and was a prisoner of war.

"I'm here to honor him," said Genes, in period dress, his wife beside him in a long purple dress and black lace gloves.

Not all South Carolinians backed secession. About 703,000 of them, 57 percent of state residents in 1860, were slaves. A few whites opposed it, including lawyer and politician James Petigru, who said: "South Carolina is too small to be a Republic, and too large to be an insane asylum."

The men who voted, 169-0, on Dec. 20, 1860, to take South Carolina out of the union set in motion events that reverberate today.

The decision led to a war that killed nearly 2 percent of the nation's population - 600,000 people. That's roughly the total of American deaths in all of the other wars the country has fought and would be the equivalent of 6 million Americans dying today.

On the eve of the Civil War, census data ranked South Carolina third in wealth among the states. In 2008, its per-capita income was 45th.