The six foundational principles of the United States Constitution are generally held to be those of limited government, republicanism, federalism, a system of checks and balances, separation of powers, and popular sovereignty.
It is clear that two of these principles, the system of checks and balances and the separation of powers are primarily a means of achieving one of the others—limited government. Similarly, one might regard another two, republicanism and federalism, as ways of protecting popular sovereignty. The principles of limited government and popular sovereignty, therefore, are more important than the other four.
If one asks why limited government and popular sovereignty are important, the answer is substantially the same in both cases. Both protect the freedom of the people. However, they do this in different ways. Popular sovereignty guarantees that the people rule, rather than a tyrant. The United States is not ruled by a ruler, but presided over by a president. Power, at least in theory, remains with the people and is exercised by the institutions of government on their behalf.
Limited government, however, restrains even the power that is actually or ostensibly employed on behalf of the people. It is, therefore, more important than popular sovereignty, since it prevents even the people, or those claiming to act for the people, from acting tyrannically towards the individual. Limited government does more than any other constitutional principle to preserve freedom.