How did the church demonstrate power in the middle ages?

Well, I think In the middle ages, the government or whoever as ruling would enforce laws of religion on people. Some people secretly ran away from it, but others stick to it like glue. Hope this helped.

Ithink it iscommunism?

Assemblies do not have written codes of laws. laws are matters for magistrates and courts, not assemblies. codes of law are things such as civil law, criminal law, and constitutional law. what assemblies have are procedures regarding debating, voting and other business they might carry out.  also note that rome had three assemblies: the assembly of the soldiers, the assembly of the tribes, and the plebeian councils.