San Francisco System
The San Francisco System (also known as the "Hub and Spokes" architecture) is a network of bilateral alliance pursued by the United States in East Asia, after the end of the World War II - the United States as a 'hub', and Japan, South Korea, the Philippines, Taiwan, and Australia as 'spokes'. The system is made of political-military and economic commitments between the United States and its Pacific allies. It allowed the United States to develop exclusive postwar relationships with the Republic of Korea (ROK), the Republic of China (ROC or Taiwan), and Japan. These treaties are an example of bilateral collective defense. Since the system emerged under the U.S powerplay rationale, it is the most dominant security architecture in East Asia up to now.
Hub-and-spokes system, with the United States as the "hub" and no apparent connections between the "spokes" allowed the U.S to exercise effective control over the smaller allies of the East Asia. The legacy of the system is continuing until today, represented by the absence of the multilateral security architecture in the region like NATO. Some argue that the reason why the hub-and-spoke network remains viable today is because its focus moved from regional concerns to those of the global such as, the War on Terror and issues dealing with WMD.
Right after World War II United States was not interested in being involved in East Asia and was more concentrated in its role in Europe. However after the Korean War, the US became more engaged in North East Asia.
The US started building its bilateral relations in East Asia with Japan. At the San Francisco Conference in September 1951 the US signed the US-Japan treaty of Mutual Cooperation and Security. Later on it moved to sign a Mutual Defenses Treaty with the Philippines in August 1951, the US-Republic of Korea Defense treaty with Republic of Korea in October 1953, and the US-Republic of China security treaty with China in December 1954. With these treaties the US was able to construct the Hub and Spokes System.
Victor Cha explains the reason for the US’s choice for a bilateral structure with the powerplay theory. The underlying idea came from the Domino Theory – that if one nation falls into communism others will follow. He defines powerplay as 'the construction of an asymmetric alliance designed to exert maximum control over the smaller allies in the region that might engage in aggressive behavior against adversaries that could entrap the United States into an unwanted war.' In other words, the hub and spokes system allowed the United States to not only contain the Soviet threat but also have exclusive power over the East Asia. With this system the US would be able to control of the rogue allies (rogue state) – anticommunist dictators who might start wars for reasons for domestic legitimacy (political) of their own regime. The US had a fear that it may be entrapped in an unwanted war, thus needed a way to contain these rogue allies. An example of a rogue ally is Syngman Rhee of South Korea. Due to his ambitions to unify the Korean peninsula, the treaty would contain his adventurism. Another is Chiang Kai-Shek. His ambition to overtake mainland China heightened the fear of entrapment to the US. Another reason for the U.S. in taking bilateral agreements in the region was to assure the nations in the region against the revival of Japanese aggression and at the same time, assisting Japan for its economic recovery, in order for it to become a growth engine of the region by giving enough economic opportunity (a direct contrast to the Treaty of Versailles between the WWI Allies and Germany, which forced Germany to compensate for the massive destructions it had caused, leading to its early collapse.)
The Hub and Spokes System is a highly asymmetric alliance by nature in both security and economic dimensions, offering military protection and economic access through trade rather than aid. The system can best be explained through the lens of the security-autonomy tradeoff model. The model accounts for asymmetrical alliance ties involving states of different power status than for symmetric alliance bonds. An asymmetric alliance is a contract in which the major power takes on the responsibility for a minor country's security by pledging to support it in the contingency of military conflict. In return, the major power gains autonomy or influence over the minor power's foreign policy decision-making process.
The rationale for the spokes to entering this system can be explained as minor powers may seeking alliances in order to increase security from military aggression. While major powers may be interested in alliances with minor powers, not to defend its own territory, but to extend their sphere of military and foreign influence.
It is important to note that the nature of the relationship was a bit different with Japan from other East Asian countries. The US viewed Japan as a possible great power in East Asia. Thus, the US constructed the strongest defense treaty with Japan. The US wanted Japan to be more involved and share the burden in peace keeping in Asia. However, the Yoshida Doctrine shows that Japan did not share the same ideas.
However, over the years, East Asian nations began to recognize the value of multilateralism and began forming indigenous multilateral security mechanisms, which the U.S. is not a member of, such as the ARF (1994), ASEAN, APEC. But, these are merely considered as venues for ‘talks’ about various security issues but having no concrete plans for execution. One of the causes of this phenomena is due to the 1997 Asian financial crisis, where some regional states realized the importance of an ‘exit/entry option’ for regional economic stability aside from the U.S. This has been characterized as a challenge to the U.S.-led hub-and-spokes system, as the nations in the region increased their interactions with China, making the bilateral alliances as a hedging option. 
- Victor Cha, "Powerplay: The Origins of the U.S Alliance System in East Asia," International Security 34(3) (2001/10). Powerplay.
- Park, Jae Jeok. “The US-Led Alliances in the Asia-Pacific: Hedge against Potential Threats or an Undesirable Multilateral Security Order?” The Pacific Review, vol. 24, no. 2, 2011, pp. 137–158.
- Calder, Kent. “Securing Security through Prosperity: the San Francisco System in Comparative Perspective.” The Pacific Review, vol. 17, no. 1, 2004, pp. 135–157
- Tan, See Sang (2004). Asia-Pacific Security Cooperation: National Interests and Regional Order. M.E. Sharpe. p. 9.
- Kent E.Calder, "U.S Foreign Policy in Northeast Asia," in Samuel Kim, ed. The International Relations in East Asia (Lawman & Littlefield, 2004). Key traits of the San Francisco System.
- Kim, Samuel S. (2004). The International Relations of Northeast Asia. Rowman & Littlefield. pp. 226, 227, 228.
- Volker Krause, J. David Singer, Minor Powers, Alliances, And Armed Conflict: Some Preliminary Patterns .
- Bennett, D. Scott. 1997. “Testing Alternative Models of Alliance Duration, 1816–1984.” American Journal of Political Science 41:846–78. Asymmetric alliance.
- Andrew Carr and Joanne Wallis (2016). Asia-Pacific Security: An Introduction,. Georgetown University Press. pp. 109, 110.