From an article on Sudan divestment in the Ethical Corporation:
“Sudan is not South Africa,” Ahmed says. “Divestment did not cause the demise of apartheid; economic and political realities in South Africa did.”
Steven Bainbridge, a corporate law professor at UCLA, agrees and says social activist divestment tends to have little impact on its targets, but does reduce returns to investors who divest.
They're quoting, I assume, from my post UC Regents Decide to Divest from Sudan, which links to earlier TCS columns and blog posts on divestment.