Many political scientists believe that separation of powers is a decisive factor in what they see as a limited degree of American exceptionalism. In particular, John W. Kingdon made this argument, claiming that separation of powers contributed to the development of a unique political structure in the United States. He attributes the unusually large number of interest groups active in the United States, in part, to the separation of powers; it gives groups more places to try to influence, and creates more potential group activity. He also cites its complexity as one of the reasons for lower citizen participation.[citation needed]

What does John W. Kingdon attribute the small number of interest groups in the US to?