For a number of reasons ​ — including drought, economic crises, civil unrest, and war — ​ “inefficiencies and service breakdowns do occur with great frequency, ” states Feeding the Cities, published by the Food and Agriculture Organization of the United Nations (FAO).
وتشير التقديرات الى انه بحلول سنة ٢٠٠٧ ،‏ سيعيش اكثر من نصف سكان العالم في المدن .‏