When Rome fell, Europe fell into a state of constant warfare. ... Feudalism also further weakened trade and economic development in Europe. Serfs who worked the land were bound to the land, and forbidden to create economic infrastructure without their lord's permission.
Answer:
first awnser I looked it up
It is Tokyo that has the world's most populated urban center. Indeed Japan itself has a very condensed population since there is so little land relative to the population.