Federalism Federalism is a system of government that divides power between a national government and a regional government with the use of a constitution. Throughout the United States history, federalism has played a significant role in the constitution and the system of government adopted by the United States of America. Federalism has also changed throughout the course of America’s history to fit the constitution and the government. Montesquieu was a French philosopher who was very important in the American constitutional thought. He was a man who was referred to more that any other theoretical writer and wrote, "The Spirit of the L