WASHINGTON — Wal-Mart donated $5 million Tuesday to help build the Smithsonian Institution’s planned National Museum of African American History and Culture on the National Mall.

The gift makes the world’s largest retailer one of the project’s “founding donors” who have given more than $1 million.

Construction is scheduled to begin next year for a $500 million museum on a five-acre site near the Washington Monument next year. The project is on track to open in fall 2015, Museum Director Lonnie Bunch said Tuesday.

“This opens the door for even more corporations to give money and give support,” Bunch said of Wal-Mart’s gift. “We’re looking for entities that care about questions of diversity and education in America’s history.”...