"It took a hurricane to speed up and really jump-start the reform efforts in New Orleans, " says Gary Robichaux, principal of McDonogh 15 (named for a slave owner who over a century ago left an endowment for building public schools in New Orleans).

FORBES: Katrina's Surprise

But in present-day Ghana, then called the Gold Coast, there were over 30 more slave forts, built and maintained by almost all of the European trading powers of the day: the Swedes, Danes, French, British, Dutch and Portuguese.

ECONOMIST: Slavery

The concept of depreciation is also credited to the railroad era, when railroad owners allocated the cost of their trains over time, but Rosenthal notes that slave owners were doing this before then.

FORBES: The Messy Link Between Slave Owners and Modern Management

Some of Congress's fiercest fights were over the admission of new states to the union, and whether they should be slave or free.

ECONOMIST: American democracy