Environmental degradation causes stress in individuals and groups, especially through a scarcity of resources. When political processes within a nation are unable to handle the effects of environmental stress, such as those resulting from erosion and desertification which lead to the marginalization of sectors of the population, this can lead directly to violence. A number of factors affect the connection between environmental stress, poverty, and security, such as inadequate development policies, adverse trends in the international economy, inequities in multi-racial and multi-ethnic societies, and pressures of population growth. Environmental stress, such as burned fields and forests, may be both a cause and a result of military conflict between nations, and add to the human distress of the other consequences of war.
As the global population continues to grow, there is increasing pressure to develop agriculture, roads and transportation systems in previously unsettled areas. This kind of land conversion can encourage the spread of diseases harmful to human health. For example, leishmaniasis, an infectious disease transmitted through a sandfly bite, has increased to 12 million cases (WHO 1998) each year alongside increasing land development in Africa, Latin America and West Asia (WHO 1997b). Forest clearance in particular is associated with higher incidence of diseases such as malaria.
In 1996 it was reported that some 80 countries comprising 40% of the world's population are suffering from serious water shortages; in many cases, the shortage has become the limiting factor to economic and social development. 1.2 billion poor people, more than one-fifth of the world's population, live in countries facing what is termed 'medium-high to high water stress'.