Purpose: By analyzing the res judicata principle and the fork-in-the-road clause, which are frequently at issue in international commercial arbitration, this study presents the implications related to these clauses after analysis of Iberdrola v. Guatemala (II).
 Research design, data, and methodology: This study mainly adopts the literature research method, and utilizes domestic and foreign literature as well as Internet data.
 Results: ① The issue of res judicata was decided based on international law and the law of the place of arbitration (Swiss law). ② Based on the triple identity test, the ICSID recognized the arbitration’s denial of jurisdiction under the res judicata principle, and the UNCITRAL claimant was blocked in arbitration.
 Conclusions: It is meaningful that it was decided that the respondent country does not have the right to file a counterclaim, saying that the former takes precedence in cases where the investment treaty and the arbitration rules contradict each other.
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