In what way was christianity a unifying force in medieval europe

One of the main ways in which Christianity was a unifying force in medieval Europe is that the Catholic Church was in charge of practically all matters concerning the state--meaning that in order for people to live even semi-prosperous lives they had to adhere to church doctrine. 

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.