Across the Middle East and North Africa (MENA) four countries (Egypt, Libya, Tunisia and Yemen) experienced regime change during the Arab Spring uprisings. Scholars argue that a primary reason why regime change occurred was due to the behavior of the military (Barany 2011; Bellin 2012; Lutterbeck 2012). When a government faced mass political protest did the military support the incumbent regime or the protestors? What caused this variation in military behavior? Recent literature has pointed to multiple factors causing this variation including economic self-interests (Goldstone 2011), the size of the social movement (Bellin 2012), ethnic affiliation (Barany 2011) and international actors (Nepstad 2013; Goldstone 2013). While these previous explanations are informative I argue that in order to more fully understand Arab military behavior during the Arab Spring it is important to also examine the relationship between the military and internal security forces (ISF) and the role of the military in relation to the entire state security apparatus. I broadly define security apparatuses as the entire collection of a state’s security forces that range from external security, internal security, intelligence, paramilitary and policing. I argue that across the region the relationship between the military and the larger state security apparatus varies and that different security apparatus structures help explain the divergent behavior demonstrated by Arab militaries during the Arab Spring. I posit that certain security apparatus structures allowed some militaries to more easily defect against the regime and support protestors, whereas other security apparatus structures made it institutionally difficult and costly for militaries to defect against the regimes.