Carnegie began his activities in philanthropy after he retired in 1901, at the 66 as the world richest man, wanting to become a philanthropist. Carnegie did so because of his belief in the "Gospel of Wealth," meaning that he believed that those who were wealthy were morally obligated to give/donate their money to a cause that puts it back into the community and society. He supported: education (Giving to towns and cities to build more than 2,000 libraries, as well as giving $125 million to the foundation known as the Carnegie Corporation to Aid Colleges and other schools); world peace (Establishing the Carnegie Endowment for International Peace, and funded the building of the Hague Palace of Peace, housing the World Court). By 1911 he would donate a huge margine of his fortune for charity, 90 percent of his fortune to be exact.
http://www.americaslibrary.gov/aa/carnegie/aa_carnegie_phil_1.html