The Supremacy Clause forms the root of what aspect of the country's government system?

I believe the answer is: The concept of Federalism

Federalism refers to the concept of government which include the creation of several states with their own autonomy accompanied with one central government to rule them all.

Because of this, supremacy clause is needed in order to ensure that the federal government has the power to overruled all regulation made by the states in case they are contradicting one another.

The Supremacy Clause forms the root of the aspect of "federalism" within the country’s government system, since it means that although power is shared between the federal government and the states, the federal government reigns supreme.