What governmental and social system that relied on land a loyalty existed in Western Europe after the fall of Rome?

Tenochtitlán was the capital of the aztec empire. it was a busy and bustling city where“there are daily more than 60,000 souls, buying and selling, and where are found all the kinds of merchandise produced in these countries.” when cortes arrived in 1519, theenormity of the trading market and the smoothness of it’s running both surprised and  impressed him.