The justification of the state refers to the source of legitimate authority for the state or government. Typically, such a justification explains why the state should exist, and to some degree scopes the role of government – what a legitimate state should or should not be able to do.
There is no single, universally accepted justification of the state. In fact, anarchists believe that there is no justification for the state at all, and that human societies would be better off without it. However, most political ideologies have their own justifications, and thus their own vision of what constitutes a legitimate state. Indeed, a person's opinions regarding the role of government often determine the rest of their political ideology. Thus, discrepancy of opinion in a wide array of political matters is often directly traceable back to a discrepancy of opinion in the justification for the state.
The constitutions of various countries codify views as to the purposes, powers, and forms of their governments, but they tend to do so in rather vague terms, which particular laws, courts, and actions of politicians subsequently flesh out. In general, various countries have translated vague talk about the purposes of their governments into particular state laws, bureaucracies, enforcement actions, etc.
The following are just a few examples.
In feudal Europe the most widespread justification of the state was the emerging idea of the divine right of kings, which stated that kings derived their authority from God and could not therefore be held accountable for their actions by any earthly authority such as a parliament. The legitimacy of the state's lands derived from the lands being the personal possession of the monarch. The divine-right theory, combined with primogeniture, became a theory of hereditary monarchy in the nation states of the early modern period. The Holy Roman Empire was not a state in that sense, and was not a true theocracy, but rather a federal entity.
The political ideas current in China at that time involved the idea of the mandate of heaven.