How can overcrowding contribute to the collapse of a civilation

I was just learning about China's one-child policy. They did this because Deng Xiaoping feared that China's farms wouldn't be able to produce enough food. Therefore, overcrowding can cause shortages of food, jobs, homes, etc. Now imagine an area that has a type of animal and because of overcrowding there are fights among the animals for food and anything that will keep them alive. Overcrowding can eventually lead to the extinction of a species because everyone and everything wants to survive. I hope this helps 

Urban growth invariably feeds increased commercialization and industrialization. it requires continually expanding land areas. when urbanization rates are high, and countries do not have the institutional and managerial capacities or economic wherewithal to manage such rapid growths, they exert intense pressure on the types and nature of the resulting settlements. they contribute to the development of overcrowded slums and shanty towns without adequate essential services and necessary infrastructure.-by asit k. biswas and cecilia tortajada

The adams apple, or laryngeal prominence. is a feature of the human neck, and is the lump or protrusion that is formed by the angle of the thyroid cartilage surrounding the larynx seen especially in males.