The occupation of Iran in September 1941, and the escape of the military and the dissolution of the Iranian army, regardless of its military and political consequences, was a blow to the image of Reza Shahi's army formed in public opinion. The uniformed army, which had been able to extensively suppress all dissident domestic groups and local movements, now collapsed strangely in the face of a foreign enemy. Understanding this failure is one of the most important questions in contemporary Iranian history. It seems that this issue should be sought in the sultanism nature of the first Pahlavi government. Therefore, the main question of this research is "How did the sultanism nature of the government pave the way for its defeat in September 1941?" To investigate this issue, using the descriptive-analytical method and collecting data by means of library research, it was found that the influence of the monarchical nature of the government on the decision-making system, military functions, and a lack of understanding of the international system, led to the defeat of the army in September 1941 before any serious confrontation. In other words, by nature, an army that like other parts of the government managed all its general and particular affairs "under the command of the monarch" could not resist the foreign enemy.