The U. S. Constitution is an important document because

The Constitution of the United States established America's national government and fundamental laws, and guaranteed certain basic rights for its citizens ... Under America's first governing document, the Articles of Confederation, the national government was weak and states operated like independent countries

Explanation:

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Answer: Constitution is important because it established the fundamental laws and principles that govern the United States of America, and outlined the individual liberties guaranteed to its citizens. It places the government's power in the hands of its citizens, noting which matters are to be decided by the federal government and which matters are left to the states.