This dissertation studies Taiwan's security sector refonn, one that intends to nationalize the anned forces and intelligence services by removing partisan political control and placing the security sector under state civilian governance. This dissertation asks why civil-military relations in Taiwan remain stable dunng this refonn process in the face of three major challenges: external threat posed by China, domestic democratization process, and organizational legacy of party-military traditions. This study posits that all three conditions facilitate military subordination to civilian control, but at the same time each presents certain challenges for the shaping of an apolitical security sector. Interviews with military and intelligence officers and analyses of personal memoirs of relevant government officials fmd that party-army traditions have facilitated the military subordination willIe undermining the endeavors to depoliticize the military. ]n contrast to conventional wisdoms, the threat environment is the least powerful factor in the explanation of stabilized civil-military relations in Taiwan. On the other hand, democratic transition and consolidation have best contributed to the institutionalization of civilian control and the cultivation of an apolitical ethos. Finally, this study also finds that interactive effects of the three conditions are at work in stabilizing civil-military relations when the security sector faces difficult decisions. Most indicative is the securitization efforts that excessively heighten the threat perceptions under Taiwan's highly divided society. While civilian politicians may exaggerate the threat Taiwan faces to serve their re-election interest, security sector actors follow the civilians' political moves to satisfy their corporate interests. At the same time, security sector actors claim that they have Dot fallen back to a politicized military since they simply follow and support the civilian leaders' decisions.