History
Dual Federalism
Quick fact
The term 'dual federalism' was popularized by political scientist Edward Corwin in the 20th century, but the concept dates back to the Founding Fathers, who explicitly limited federal powers in the Tenth Amendment.
Why this is interesting
You know that the U.S. government is split between Washington and the states, but did you know this division was once imagined like a layer cake—with each level holding its own distinct powers, never mixing? What happened to make it more like a marble cake?