Which of the basic principles of our government (popular sovereignty, limited government, separation of powers, checks and balances, federalism, and judicial review) has been most effective in keeping the government the "servant" and not the "master" of the people?
In my view, this is completely a matter of opinion. If you think that this is meant to be an objective question with a single correct answer, please check your textbook or notes to see which answer you are expected to give.
For me, it is very hard to pick one of these basic principles because they are all so interconnected. It is hard to differentiate the effects that each principle has had. If I had to pick one, however, I would pick popular sovereignty.
Popular sovereignty is the idea that the people are in charge. The principle of popular sovereignty gives us the right to vote and the right to expect that the government will do what we want. Without this, I would argue, none of the other principles would mean much.
For example, what good would separation of powers do if we did not have popular sovereignty? We would have the three branches of government, each with their separate powers, but we would not have the right to tell those branches of government what to do. We would, perhaps, not even get to vote for them. The fact that we do get to vote for them is what keeps them in line. They know that if we think that they are doing things wrong, we will simply stop voting for them. We will “throw the bums out” and elect new leaders in their place. Because our leaders know that they ultimately have to answer to us, they cannot make government our master (even if they want to).