Constitutionalism refers to a political structure of a state based on the constitution, as the name itself says. A constitution is the most important legal document in a country, listing the rules and laws that everyone, be it regular people, institutions, or the president himself has to follow. Constitutionalism was created to make people equal, to protect their natural rights and guarantee them liberty in the country they live in.
On the other hand we have the divine right of kings. It is a concept which is quite opposite to that of constitutionalism. As the name itself says, the divine right of kings assumes that king was sent to earth to rule instead of God himself. Given that God doesn't have a physical presence in our world, he has chosen kings to be his representatives on Earth. Thus, the king has every right to do whatever he pleases, without having to think about constitutions, governments, or the feelings of his subjects.
I believe that America is based on the principles of constitutionalism, mostly because it never had a king, but was rather a democratic republic from the very beginning.
