Reasons of [Reza Shah’s] Confrontation with Religion and Shiite Clerics Reza Shah pursued a reformist policy since the very beginning of his rule. This policy was implemented through consultation with westernized advisors, who were devoid of any basic and indigenous mindset. As a result, there was an inevitable and serious confrontation between these policies and Islamic values. In addition, Reza Shah was essentially a person who did not believe in these values. 

Reza Shah’s reforms were actually based on three pillars:
nationalism; modernism; and concentration of power. De-Islamization and confrontation with Shiite clerics were definite consequences of these reforms.  

Reza Shah’s Nationalism
Nationalism refers to the belief and faith of the majority of people – who constitute a political community and a nation – in the right of having an independent country and their interest in getting sacrificed for this country. The Iranian nation is comprised of human beings with a culture and associated beliefs formed during centuries. However, Reza Shah’s nationalism was merely emphasizing on a part of this history and culture. His nationalism was concentrated on pre-Islamic Iran and considered Iranians as a nation separated from their current religion and ideology. After his accession to the throne, Reza Shah studied history and became interested in Zoroastrianism. Reza Shah’s regime attached great importance to its own version of nationalism. This official version of nationalism was so significant for Reza Shah that Iranian press were obliged to propagate no other versions of nationalism. Iranian press were only allowed to emphasize on the splendor and grandiose of the pre-Islamic Iran. Reza Shah’s nationalism ignored Iranian post-Islamic achievements. As a result, some scholars and authors have described his version of nationalism as "chauvinism” or "extremist” and "regressive” nationalism.

Reform-minded individuals have usually been concerned about backwardness in developing countries. Finding out the causes of this backwardness has been the greatest concern for these reform-minded people. By attaining a kind of self-consciousness, some reformists, such as Seyed Jamaledin Assadabadi, had concluded that nations could cope with this backwardness through a revival of their own norms and values. Nevertheless, many alienated intellectuals who were worried about backwardness in the society resorted to western values and norms in order to save the society from this affliction. For instance, Taghizadeh argued that westernization, from head to the toe, is the only solution for coping with backwardness in the society. Through duplicating western patterns in developing countries, these westernized intellectuals endeavored to impose some layers of western culture on their own country. Unfortunately, this procedure bore no fruit, because developing nations neither attained western civilization nor managed to maintain their own civilization. Reza Khan, too, had such a mindset. He believed that through attaining some aspects of modernism, he can produce profound developments in Iran and expose the country to an evolutionary movement. Reza Shah’s modernism was in sharp contrast with people’s religious traditions and values. Resorting to coercive force, Reza Shah endeavored to demolish religious traditions and values. At the same time, his initiatives for introducing modernism to the country were contradictory with the kind of nationalism that was propagated by him. Despite the fact that nationalism was a western phenomenon, Reza Shah endeavored to adopt pan-Iranism as the ideology of his regime. On the other hand, Reza Shah was so fascinated by western developments that strived to impose western culture on Iran. He was so extremist an individual in his adoration of western culture and civilization that in cases of contradiction between western and nationalistic norms, he gave priority to western norms. Sometimes, he even tried to portray this contradiction as a rivalry between nationalism and Islam or between nationalism and Arabism. Reza Shah’s modernism resulted in the prevalence of westernization, confrontation with religious values, and marginalization of Shiite clerics. His modernism was not a solution to Iranian people’s problems; rather, it further complicated their troubles. 

Concentration of Power
Generally speaking, crafting a top-to-the-bottom change requires its own proper instruments. Modernism in the west was imposed on states from bottom to the top. As a result, modern states in the west are outcome of the evolutionary process of modernism. On the contrary, elites in third-world nations intend to inject modernism on lower social strata in a top-to-the-bottom procedure. In order to implement such a procedure, states are required to take advantage of various instruments of power, such as suppressive armies, appropriate laws, and ready-to-obey forces. Reza Shah had access to all these instruments of power. He established a modern army through which he managed to suppress all internal riots and uprisings. However, Reza Shah’s modern army had a very peculiar characteristic: inability to resist against a powerful foreign force. As a matter of fact, this modern army could not make the slightest resistance against Allied forces and collapsed before being engaged in any direct confrontation with those forces. Reza Shah’s modern army had actually been designed for domestic suppression. 
In order to concentrate his power, Reza Shah appointed military men for most of the high-profile political and administrative posts. These military men had authority over political officials in different parts of the country. He even appointed a rigid and authoritarian military officer to superintend Tehran municipality. Governments which were formed during Reza Shah’s rule had no authority of their own. Since the sixth term of the National Consultative Assembly (the Majlis), military officials selected all deputies, except deputies from Tehran. In later terms of the Majlis, deputies were selected only from the lists presented by the government. On the other hand, suppression and settlement of tribes was another initiative by Reza Shah for further consolidation and concentration of his power. Reza Shah’s antagonism towards Shiite clerics was the consequence of his inclination for further consolidation of power. He had realized that Shiite clerics have, historically speaking, always advocated the people and religious values. Reza Shah considered clerics obstacles for the implementation of his plans. Therefore, he pursued a policy of gradual isolation of Shiite clerics.

Reference: An Introduction to Islamic Revolution in Iran