But you cannot escape the fact that the Catholic Church is a kingdom of this world, although Christ said that His Kingdom was not of this world.

The Catholic Answers

The Catholic Church is not a kingdom of this world. It is the Kingdom of Christ in this world. And the Pope as Pope is not monarch of the Church in any national sense. No national considerations sway his rule over the millions of Catholics of every race and clime. He has temporal authority to-day in Vatican City, but that is merely that he may secure complete immunity from the interference of worldly powers.

Radio Replies Volume 1 by Rev. Dr. Leslie Rumble MSC and Rev. Charles Mortimer Carty