The conquest of Iran by Muslim Arabs is one of the most important developments in Iran's history. Iran was completely conquered over two decades and the Sassanid government collapsed. There are still a lot of questions about this fall and its reasons. This article, which is based on the main resources of conquest of Iran, tries to present a new model for analyzing the course of the conquests. The main question of the study thus is if the conquests followed a particular pattern and if they can be presented in the form of a single theory. The second question concerns how the cities were conquered. Were they conquered through war or peacefully? In response to the above question, the hypothesis of this paper is formed. Iran was divided into eight regions, at the borders of which, one can see the greatest resistance of the Iranian military, which we call "border-threshold resistance". Once the borders were broken, the advance of Muslim Arabs was faster and with less fighting. As a result, the clashes are mostly generated by the military, and the general public are less involved at war. Understanding the speed and the quality of the Arab conquests of Iran is subject to understanding this pattern.
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