It was "unacceptable" for Virginia's governor to omit references to slavery in declaring Confederate History Month in the state, President Barack ObamaBarack Hussein ObamaGeorge W. Bush honors father at benefit for hurricane victims Dem senator: ‘I miss every one of’ our last 5 presidents All five living former presidents appear at hurricane relief benefit concert MORE said Friday.

The president said that while he thought it was important for Americans to be familiar with the history of the Confederacy, it was impossible to see the full picture without studying the institution of slavery.

"I don't think you can understand the Confederacy and the Civil War unless you understand slavery," Obama said during an interview on "Good Morning America" on ABC. "And so, I think that was an unacceptable omission. I think the governor's now acknowledged that."

Virginia Gov. Bob McDonnell (R) revived the Confederacy observance month, something his two predecessors in office, both Democrats, had declined to do.

McDonnell found himself caught in a firestorm, though, after his declaration made no reference to slavery, an omission that aides had seemed to dismiss in the immediate aftermath. The governor has since apologized, and added references to slavery.

"I think it's just a reminder that when we talk about issues like slavery that are so fraught with pain and emotion, that, you know, we'd better do so thinking through how this is going to affect a lot of people," Obama said. "And their sense of whether they're part of a commonwealth or part of our broader society."