After working three years as an assistant editor for The Papers of Andrew Johnson, based at the University of Tennessee, Simpson joined the faculty at Wofford College in Spartanburg, South Carolina, in 1987.

Three years later, in 1990, he migrated west to Arizona State University, where he presently teaches.

The latter was a New York Times Notable Book and a Choice Outstanding Academic Title for 2000.

[2] In 2009 the U.S. State Department asked him to travel to Turkey for two weeks to lecture on Abraham Lincoln and Barack Obama in historical context.

After serving four years as one of the contributors to the prize-winning "Civil Warriors" blog,[3] in late 2010, Simpson started his own blog, "Crossroads", where he discusses the American Civil War and offers critiques of negationist neo-Confederate and Lost Cause claims regarding the war.