Obama cited inflammatory remarks made by his pastor that are now being used as political ammunition against him - remarks that Obama has denounced.
"If all I knew were those statements I saw on television, I would be shocked," Obama said.
Obama suggested that more and more is being made of racial divisions as his contest with Sen. Hillary Rodham Clinton heats up.
"The forces of division have begun to raise their ugly head again," Obama said.
"It reminds me: We've got a tragic history when it comes to race in this country. A lot of pent-up anger and mistrust and bitterness. This country wants to move beyond these kinds of things."
The Illinois senator's comments came a day after he denounced statements appearing on television and on the Internet by the Rev. Jeremiah Wright, pastor of the Chicago church Obama joined nearly 20 years ago.
Obama said that pointing out racial differences only makes it harder to "deliver on the big issues we face in this country," which he said include health care, the slumping economy, terrorism and caring better for veterans.
Obama, whose mother's family was from Kansas and his father from Kenya, said he was speaking "as someone who has little pieces of America in me."
He said schools should do a better job of teaching all students African-American history "because that's part of American history," as well as women's struggle for equality, the history of unions, the role of Hispanics in U.S. and other matters that he suggested aren't given enough attention.
"I want us to have a broad-based history" taught in schools, he said, even including more on "the Holocaust as well as other issues of oppression" around the world.
Obama spoke in the gymnasium of Plainfield High School, near Indianapolis, as he directed his political attention at states beyond the critical April 22 Pennsylvania primary.
"We are going to be campaigning actively in Indiana," Obama said to cheers. Indiana and North Carolina have primaries on May 6, two weeks after Pennsylvania.
