In contrast to the prevailing view that America's strategic ambiguity (SA) policy in the Taiwan Strait started with the Nixon and Carter administrations, this dissertation posits that policy actually began with the Truman Presidency. I wish to address why the Truman administration had rejected the option to recognize the People's Republic of China (PRC) and abandon Taiwan and instead chose a complicated SA policy. This project relies upon qualitative case studies and uses primary and archival sources to analyze the thoughts of top Truman administration officials. The finding suggests that SA was chosen and implemented because it resonated with the ideas and norms of Wilsonian Open-Door internationalism. In the context of 1949-50, establishing diplomatic ties with the PRC and acquiescing to its engulfment of Taiwan would be unpalatable to the Wilsonian liberalism. Even today, SA allows Washington to continue safeguarding Taiwan's freedom and autonomy and engaging China, thus enticing her toward liberalization and democratization.