The new Constitution took effect on March 4, 1789. That same year, Congress wrote and proposed twelve amendments to the Constitution. Three-fourths of the states would have to ratify these amendments in order to add them to the Constitution. The states ratified ten amendments on December 15, 1791. Together, they became the Bill of Rights. The Tenth Amendment set the guidelines for federalism in the United States. It said that any powers that the Constitution did not give to the federal government belonged to the states. This was meant to calm people's worries that the federal government would try to take more and more power from the states.