However, the departure from this view became evident with the ratification of the Sixteenth Amendment to the United States Constitution (income tax) as well as the Seventeenth Amendment to the United States Constitution (direct election of federal Senators).
-Wikipedia
What ended the era of dual federalism?
2 answers
This site may have the information you need.
http://en.wikipedia.org/wiki/Dual_federalism#Departure_from_this_view
http://en.wikipedia.org/wiki/Dual_federalism#Departure_from_this_view