The purpose of the Supremacy Clause, found in Article VI, Clause 2 of the U.S. Constitution, is primarily to establish the Constitution as the supreme law of the land. This means that federal laws and treaties take precedence over state laws whenever there is a conflict. Therefore, the correct answer to your question is:
To establish the Constitution as the law of the country.
This clause helps to create a cohesive federal legal system where federal law is dominant, ensuring consistency across states.