While farmers have faced droughts for millennia, it is only recently that dry years result in widespread famine. Formerly, in good years, a farmer would fill grain stores with enough to survive for several consecutive seasons. Grazing was done considering available pastures and water holes so over grazing was avoided. Fields were left fallow for long periods to enable the soil to recover. This balance has been disrupted by a number of things. Veterinary medicine by treating animals has resulted in vast herds with little grass. Mechanical pumps increase the use of water creating the likelihood of drought. Demands for market crops because of pressures for exports and encourage short term thinking. Grain silos are emptied eliminating buffers against famine. The land is no longer left fallow and the soil becomes exhausted.
Major examples have been associated with experiments in centralized planning including the famine in the Ukraine in 1932-1933 (estimated 5 million died) and that in China following the Great Leap Forward programme in 1960 (conservative estimate that 20 million died).