What is the most important difference between the U. S. Constitution and state constitutions?

State constitutions are subordinate to the U.S. Constitution.

Explanation:

The question of the power of State and the federal government was importance for the founding fathers of the constitution of the United States. It was the weakness of the Congress that led way to framing a new constitution but there was a section that believed that the power of the federal government should not become absolute. This problem was solved by inserting the Supremacy Clause in the constitution that declares that in the cases of conflict between the two, State Constitutions are subordinate to the U.S. Constitution.