In my 2 cent opinions, armed conflict b/w countries doesn't affect too much on wildlife (as you mentioned Korean Demilitarized Zone.) However civil war in the society may declined wild life population. During civil war economy of the country goes down, people don't find any thing to eat due to poverty and less resources, as a result they don't spare any animal. Other big reason might be Population growoth, low income of people/poverty, low resources of food, urban development, mining, diminishing of natural forest,industrialization, using of pesticides etc.