WASHINGTON (AP) ― President Barack Obama ― the first black U.S. president ― heralded a new national black history museum as “not just a record of tragedy, but a celebration of life’’ as he marked Wednesday’s groundbreaking of the long-sought-after museum on the National Mall.

Obama said the National Museum of African American History and Culture “has been a long time coming.’’

“It was on this ground long ago that lives were once traded, where hundreds of thousands once marched for jobs and for freedom,’’ Obama said. “It was here that the pillars of democracy were built, often by black hands.’’

The 19th museum in the Smithsonian Institution will tell the history of black life, art, and culture and explore stories that have sometimes been left out. There will also be a court for quiet reflection, Museum Director Lonnie Bunch said.

“We will have stories that will make you smile and stories that will make you cry,’’ he told The Associated Press. “In a positive sense, this will be an emotional roller coaster, so you want to give people chances to reflect and to think about what this means to them.’’

The museum is scheduled to open in 2015. Congress pledged to provide half the $500 million construction cost, and about $100 million has been raised in private funds including gifts from Wal-Mart, American Express, Boeing, the Bill and Melinda Gates Foundation and celebrities such as Quincy Jones and Oprah Winfrey.

The future museum already has a gallery at the Smithsonian’s American history museum with rotating exhibits. The newest one explores Thomas Jefferson’s lifelong ownership of slaves and his conflict and advocacy against slavery, while looking at the lives of six slave families who lived on his Monticello plantation in Virginia.

Telling such stories has been taboo at many museums in the past. Bunch said that by presenting a fuller view of history and dealing directly with difficult issues like race, the Smithsonian can present a fuller view of history and what it means to be an American.

The staff is working to collect more material on popular culture and music, earlier materials from military history from World War I and earlier and artifacts to tell stories from the 19th century, including slavery and post-Civil War Reconstruction.