From the National Archive's website: "The Constitution acted like a colossal merger, uniting a group of states with different interests, laws, and cultures. Under America's first national government, the Articles of Confederation, the states acted together only for specific purposes. The Constitution united its citizens as members of a whole, vesting the power of the union in the people. Without it, the American Experiment might have ended as quickly as it had begun."
National Archives: https://www.archives.gov/