Catechism of the Catholic Church

If authority belongs to the order established by God, "the choice of the political regime and the appointment of rulers are left to the free decision of the citizens." The diversity of political regimes is morally acceptable, provided they serve the legitimate good of the communities that adopt them. Regimes whose nature is contrary to the natural law, to the public order, and to the fundamental rights of persons cannot achieve the common good of the nations on which they have been imposed.