The twelve-day Iran–Israel war in June 2025 transformed the Middle East. This study aims to examine the war’s impact on U.S.–China geopolitical competition in the Middle East and addresses the following question: How did the twelve-day Iran–Israel war affect U.S.–China geopolitical competition in the Middle East? To answer this question, the study employs Stephen Walt’s Balance of Threat theory, which explains states’ behavior in response to perceived threats. The research hypothesis is based on the argument that the twelve-day war, by altering the threat perceptions of the Gulf states and highlighting the functional differentiation between the United States (security–military) and China (economic–diplomatic), brought the pattern of geopolitical competition between the two powers in the Middle East into sharper relief. The findings indicate that the war altered the threat perceptions of the Arab Gulf states, reinforced the U.S. security role, and sustained China’s cautious approach. These states adopted a pattern of simultaneous reliance on both powers, although a definitive reconfiguration of the pattern of competition cannot be empirically established. This study employs a descriptive-analytical approach and is based on Stephen Walt’s Balance of Threat theory.