Pacta sunt servanda is a legal term in Latin, which refers to the continuity of agreements between parties and bindingness of the clauses for both parties regardless of a change of a government or ruler. It is one of the ordering principles of modern international law and diplomacy.

Respublica Christiana was how this collective identity called, although it never turned into an acquired state structure.

Most significant and novel concept of medieval Europe is the term nuncius. A nuncius is the person in charge who is appointed by the ruler as the voice of the principal in another political entity.