City

Cities consume so much energy that the number of cities that can exist on Earth is limited. In other words, the bottleneck for cities is not land but energy, so not all territory can become urbanized. This is why multiplanetary expansion is necessary. Even when a country tries to create sub-cities, people are reluctant to move from established areas, leading to centralization, not only because of the energy required to build new cities but also because energy itself is limited