In the 1890s, he forged an agreement with his British competitors to divide the market, with Duke controlling the American trade, the British companies controlling the trade in British territories, and a third, cooperative venture between the two - the British-American Tobacco Company - controlling the sale of tobacco to the rest of the world. During this time, Duke was repeatedly sued by business partners and shareholders. In 1906, the American Tobacco Company was found guilty of antitrust violations, and was ordered to be split into three separate companies: American Tobacco Company, Ligget and Myers, and the P. Lorillard Company.
In 1892, the Dukes had opened their first textile firm in Durham, North Carolina that was run by Benjamin Duke. At the turn of the century, Buck Duke organized the American Development Company to acquire land and water rights on the Catawba River. In 1904, he established the Catawba Power Company and the following year he and his brother founded the Southern Power Company which became known as Duke Power, one of the companies making up the Duke Energy, Inc. conglomerate. The company supplied electrical power to the Duke's textile factory and within two decades, their power facilities had been greatly expanded and they were supplying electricity to more than 300 cotton mills and other industrial companies. Duke Power established an electrical grid that supplied cities and towns in the Piedmont Region of North and South Carolina. Lake James, a power-generating reservoir in Western North Carolina, was created by the company in 1928 and named in Duke's honor.
In 1911, the United States Supreme Court upheld an order breaking up the American Tobacco Company's monopoly. The company was then divided into several smaller enterprises, of which only the British-American Tobacco Company remained in Duke's control. After his death in 1925, there was a great deal of controversy, and some historians suspect that some resentful Imperial Tobacco executives were feeling some anger at Duke for having lost the Tobacco War between Duke's company and Imperial Tobacco.
In December 1924, Duke established The Duke Endowment, a $40 million trust fund (about $430 million in 2005), some of which was to go to Trinity College. The University was renamed "Duke University" in honor of his father.
On his death, he left approximately half of his huge estate to The Duke Endowment which gave another $67 million (about $725 million in 2005) to the trust fund. In the Indenture of Trust, Duke specified that he wanted the Endowment to support Duke University, Davidson College, Furman University, Johnson C. Smith University; not-for-profit hospitals and children's homes in the two Carolinas; and rural United Methodist churches in North Carolina, retired pastors, and their surviving families.
The remainder of Duke's estate, estimated at approximately $100 million (about $1 billion in 2005), went to his twelve-year-old daughter, Doris, making her literally "the richest girl in the world. Doris sued her mother for control of the Duke Farms estate and won. Associating Duke Farms with fond memories of her father, Doris Duke made few major changes to the property other than the adaptation of her father’s Conservatory to create Display Gardens in his honor . These Gardens showcased her father's extensive sculpture collection and were open to the public from 1964 until closed by her Foundation Trustees in May 2008.