[kjvail]

Subsidiarity -

"a community of a higher order should not interfere in the internal life of a community of a lower order, depriving the latter of its functions, but rather should support it in case of need and help to coordinate its activity with the activities of the rest of society, always with a view to the common good."

Centesimus Annus

has always been the guiding principle thought of Catholic political theory. While the authority of the Emporer and the Pope was very broad, their power was strictly limited. Your average King could hardly enforce his will outside the boundaries of his castle, he had to rely on the voluntary submission to his authority. The Emporer himself was tightly bound by the law as to what he could and could not do, the various kingdoms that made up the H.R.E. would not countance interference in their local affairs.

[annalex]

Also see Rerum Novarum, the encyclical that defined the Catholic teaching of subsidiarity, that I posted a few years back in four separate threads.

Rerum Novarum [1-15, Man and Property]
Rerum Novarum [16-30, The Church, the Rich, and the Poor]
Rerum Novarum [31-47, The State]
Rerum Novarum [48 - End, The Civil Society]