Humans are at times close to the Animal nature in times of stress. When resources are in short supply,in some countries, and your neighbors have a more abundant amount,then as happens from time to time,the country that has little attacks the country with more. These they are predicting as water and other necessity's become scarce because of global warming,we will see wars break out,and large groups migrating like we now see from the War in Syria,but it may be in a much larger amount.