Military modernization is a constant process. Securing the state and protecting its citizens are the first tasks of any government. Militaries are vital to achieving these objectives, even though they are not the only means for doing so. Moreover, wise governments recognize that security is not absolute and that actions taken by one state can create insecurity in neighbors and potential adversaries, triggering an ugly spiral that can destabilize a region. This "security dilemma" is a staple of international relations theory — and increasingly appears to describe developments in Northeast Asia.
Governments upgrade armed forces for many reasons: New technologies become available. Old weapons degrade. New threats emerge. International roles and missions evolve, requiring new capabilities. Rising status demands bigger, shinier weapons. Sometimes a government just wants to keep up with its neighbors and rivals.
The evolution of Japan's Self-Defense Forces is driven by several of these factors: New capabilities derive from new technologies; the realignment of U.S. forces in Japan create new demands; and new roles and missions result from a recalibration of responsibilities within the alliance.