What evidence supports the idea that the Church functioned like a kingdom?

The evidence that supports the idea the the Church functioned like a kingdom is the Pope, the leader of the worlwide Catholic Church, acted like a king with an official court that had diplomats and collected taxes.

The power of the pope was extended because the Church has its own court, tax system, and diplomats.

After the Crusades, the power of the popes were lessened while the power of the kings increased.