Providing an answer to the question that why the Qajar dynasty collapsed and was replaced by the first Pahlavi king, the paper is to show the existence of historical regularity in the process of power transfer. To answer the abave-mentioned question, the author examines the following hypotheses: (1) The pressure of a mumber of external and internal factors made the Qajars incapable to maintain power; (2) The simultaneosness of external and internal events were influencial on Rezakhan's power attainment; (3) The English were most influencial in the fall of the Qajars and the rise of the Pahlavis; (4) Razakhan's personal charactristics had a signifcant role in his attaining to power.
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