A Historical Basis for Force Requirements in Counterinsurgency

Abstract

Over the last eight years, one question has repeatedly come up in regard to the wars in Iraq and Afghanistan: How many soldiers are enough? The question was first raised before the Iraq war started, with highly publicized disagreements between senior military leaders regarding the number of forces needed to secure Iraq after the invasion. The debate reached another peak when the “surge” strategy was announced. It has once again become the subject of national discussion, this time with respect to Afghanistan. Despite years of debate, our understanding of force requirements for counterinsurgency has advanced little since 1995, when James Quinlivan of RAND published a seminal article on the subject. 1 The current article describes work done by the Center for Army Analysis (CAA) to better inform the discussion by examining historical data related to counterinsurgencies. The intent is not to make any policy recommendations. Nor should this analysis be interpreted to suggest that force levels alone are the key to victory in counterinsurgency. Having enough military forces is a necessary, but by no means sufficient, condition for success. The twentieth century is replete with examples of counterinsurgents winning Pyrrhic military victories that resulted in political losses. The French in Algeria and the Portuguese in Mozambique and Guinea-Bissau prevailed militarily but ultimately acceded to the insurgents’ demands for independence. The British devoted enormous forces to Cyprus and suffered relatively few losses but nonetheless had to give up control of most of the island. That said, however, force levels do matter, and history can provide a guideline for force requirements in counterinsurgency. The analysis described in this article shows that there are three major drivers of military requirements. First, as previous studies have argued and current doctrine emphasizes, security forces have to be sized relative to the population. Second, the more intense the insurgency, the more forces are required to reverse