Background: Armed conflicts include declared cross-border and internal wars and political, ethnic, and religious hostilities. The number of conflicts worldwide and their level of intensity have varied widely during the last 5 decades. Tracking conflicts throughout this period has focused predominantly on the number of individuals killed or displaced from these hostilities through count-based estimation systems, or establishing rates of excess mortality from demographic surveys. This report focuses on people living in areas with conflict by applying an estimated level of conflict intensity to data on the population of each territory with hostilities during 1946 to 2007.

Methods: Data from the Uppsala Conflict Data Program/Peace Research Institute Oslo (UCDP/PRIO) Armed Conflict project database on 324 conflicts of any type in countries with populations greater than 500 000 were combined with conflict-intensity estimates from the Center for Systemic Peace and population data from the US Census Bureau International Data Base.

Results: More than half a billion people lived in conflict-affected areas in 2007. An increasing proportion of those affected by conflict lived in early postconflict areas, where hostilities were judged or declared during the last 5 years. In the past 2 decades, the average intensity of conflict among those living in areas with a current conflict has gradually declined.

Conclusions: A burgeoning population lives in areas where conflict has recently ended, yet most of the world's large-scale medical responses to emergencies focus on high-intensity conflicts. Effective emergency and reconstruction activities in the health sector will depend on reorganizing services to increasingly focus on and transition to low-level and postconflict environments.