The nation’s largest law firms...have struggled to attract, keep and promote minority and women lawyers. Now these firms have a powerful incentive to do better: Some of their biggest corporate clients are demanding that they increase the number of minority and women associates and partners... Wal-Mart Stores has dropped two law firms...because of unhappiness with the firms’ lack of diversity... The recent corporate effort to push law firms to improve their diversity record began with Roderick A. Palmore, general counsel at Sara Lee, who wrote his peers at the top of corporate law departments to commit themselves to “end or limit our relationships with firms whose performance consistently evidences a lack of meaningful interest in being diverse.”... About 100 companies, including American Airlines, Boeing and General Motors, have signed onto Mr. Palmore’s pledge. [refers to law firms Orrick, Herrington & Sutcliffe, Morgan, Lewis & Bockius; also refers to DuPont]