You are quite right. No city can house or feed or clothe or survive long without continuous supplies from outside.
That is the 'outside'. Ingrates in the cities don't appreciate just how much they depend on people in the country that provide the food they eat, the power they use, the water they drink and bath with, the cloth the use to clothe themselves with, or the oil and gasoline they use. They even despise the very truckers that bring them those supplies on a daily basis.
Without those continuous supplies, cities will crack up in a very short time into much worse chaos then they already are.