After diplomatic relations were broken off between the US and the Government of the Republic of China (GRC) in January 1979, the US enacted the Taiwan Relations Act, which provided the GRC with a modicum of assurance from the US about the defense of Taiwan. However, unlike the Sino-American Mutual Defense Treaty, the Act did not obligate the US to defend Taiwan. Therefore, President Chiang Ching-kuo assumed that the GRC would have to defend Taiwan on its own, and the Republic of China (ROC) Armed Forces, which had maintained the posture of retaking the mainland, was reformed into a military for homeland defense. The “defensive” weapons provided under the provisions of the Act were selected at the discretion of the US, and were therefore not always appropriate for the needs of the GRC. Accordingly, the GRC defrayed its costs through a massive reduction in army forces, which remained steeped in the ideology of retaking the mainland. The GRC then proceeded to modernize the military by establishing an independent development and production system for weapons in addition to procuring them from outside the US. Forced to respond to the expiration of the Sino-American Mutual Defense Treaty—the biggest security crisis that the nation had faced—President Chiang Ching-kuo practically “abandoned” the mission of retaking the mainland. However, as the military strategy of unity of offensive and defensive remained, the ROC Armed Forces were transformed into a military for the defense of Taiwan, with a mission to retake the mainland based on this strategy.