Why did the Palestinian Authority established in 1994 create 12 security forces when Eritrea, which achieved independence in 1994, made do with one conventional army? This article attempts to explain the variation in the structure of national security systems in Third World states as a function of two basic factors: the state's political and social heterogeneity and the state's relative importance to US foreign policy and security concerns. Authoritarian one-party and centralizing states tend to fragment their security forces more than states that cultivate social or political pluralism. Fragmentation is a classic exercise of divide and rule. But a tradeoff exists between fragmentation and assuring internal security on the one hand, and ensuring offensive capabilities to ward off external enemies, on the other. Hence the importance of a strong foreign ally - preferably the United States. According to this model, centralized homogenous states enjoying US protection will tend to fragment or bifurcate their security systems most.