When former Microsoft head Bill Gates and Berkshire Hathaway chief executive Warren Buffett launched the Giving Pledge in 2010, the billionaires established a new threshold for big-donor philanthropy. Their initiative asks wealthy people worldwide to contribute most of their net worth to philanthropic causes.

Among those accepting the challenge: Facebook chairman Mark Zuckerberg and his wife, Priscilla Chan. Like Gates and Buffett, they’re following an American tradition: building a fortune and using it to serve others.

Zuckerberg and Chan recently pledged $3 billion to help cure, prevent or manage all disease by the end of the 21st century. Their pledge mirrors the ethos of 19th-century steel magnate Andrew Carnegie, who believed in giving back to the society that empowered his rise.

“Philanthropists have provided what an observer once called ‘social venture capital,’ says Leslie Lenkowsky, a philanthropy expert at Indiana University. Frequently, he adds, they invest “in innovations in health care, education, economic development, human rights and much more that governments were unwilling, unable or too short-sighted to try. As a result, men, women and children throughout the world now benefit from the generosity of people they never knew.”

Infographic with timeline of charitable giving in U.S. (State Dept./Sara Gemeny Wilkinson)
(State Dept./Sara Gemeny Wilkinson)