身為「分裂國家」之中華民國，在其「正當性」不斷流失的1960、1970年代，究竟如何面對與盟邦間之主權爭端？筆者擬以1955-1975年中華民國與越南共和國在西、南沙之交涉為題，據以檢視冷戰時期中華民國之外交行為模式，從而洞悉其對外政策自「零和外交」轉變至「務實外交」之背景。經研究後，筆者提出以下5點結論：一、中華民國在對越交涉西、南沙主權過程中，不斷出現為權衡「民族利益」及「反共邦誼」左支右絀之現象；二、在難以兼顧「民族利益」及「反共邦誼」的情況下，意味著當局必須應大局扭曲或擱置被中華民國奉為兩大外交圭臬－「正統」、「反共」之其中一項原則，進而確證了「大局外交」之假說，三、適足說明了冷戰時期「分裂國家」其「正當性」匱乏之根本性問題，是以乃有為固守其「外部正當性」或「內部正當性」而將其核心價值或基本國策（「民族利益」或「反共邦誼」）扭曲、擱置之行為；四、一旦無法兼顧「外部正當性」及「內部正當性」，當局常以「內部正當性」為依歸，足見中華民國對「正統」之需求略高於「反共」；五、由於「大局外交」顯巳動搖「正統」與「反共」作為中華民國外交指導原則之地位，故「大局外交」蓋中華民國對外政策發展中，介於「零和外交」與「務實外交」間之演化環節。前述結論亦揭示了中越間西、南沙主權交涉歷史之特殊性與價值所在。

The reality of a divided statehood that Republic of China (R.O.C) had faced by losing its legitimacy dramatically during the 1960s and 1970s raised a question of how R.O.C had dealt with issues concerning sovereignty with its allies. In attempt to answer the question and by having an insight into the transformation of R.O.C's diplomatic model happened before the late 1980s, this article has analyzed the case of the territorial issue of Spratly and Paracel Islands between R.O.C and Republic of Vietnam(R.O.V) during 1955-1975. By analyzing the case, there are five conclusions below were established. 1. The case revealed the predicament in between the national interest and the anticommunist partnership; 2. By facing the dilemma, the government of R.O.C was forced to either lay aside China's one nation idea or Anticommunism, whereas both of which were supposed to be the guidelines of R.O.C' s diplomacy. The difficult situation had verified the theory of ＂the diplomacy of the divided nation.＂ 3. The case represented the fact that a divided nation had a fundamental problem of the lack of legitimacy. In order to defend R.O.C's ＂international legitimacy＂ or ＂domestic legitimacy＂, the core values or basic national policy (＂national interest＂ or ＂anti-communism＂) was twisted or set aside respectively. 4. Once it was difficult to reconcile the demand of ＂international legitimacy＂ and the desire of ＂domestic legitimacy,＂ the authorities often preferred ＂domestic legitimacy,＂ which shows the R.O.C required ＂one nation idea＂ justly than ＂anti-communism.＂ 5. ＂The diplomacy of the divide nation＂ had obviously violated R.O.C's diplomatic guideline which regarded ＂one nation idea＂ and ＂anti-communism＂ as indispensable principles. In doing so, ＂the diplomacy of the divided nation＂ had provided a fertile ground for the new diplomacy era of Pragmatic Diplomacy since the late 1980s. The abovementioned conclusions have revealed values of both the particular history and the case of sovereignty issue s over Spratly and Paracel Islands between R.O.V and R.O.C.