When did the Constitution become the law of the land?

The Constitution became the law of the land on March 4, 1789, after it was ratified by nine states, which was the minimum requirement for it to take effect. The year 1788 marks the point at which the Constitution was officially ratified by the necessary nine states, making it valid and operational. Although the Articles of Confederation were in effect earlier, they proved inadequate for governing the growing nation, resulting in the drafting of the Constitution in 1787. The other years provided in the choices either pertain to events leading up to the Constitution or are associated with amendments rather than the Constitution's initial enactment. Thus, 1788 is the correct answer as it signifies the year the Constitution was ratified and began to assert its authority as the governing document of the United States.