At the beginning of the twentieth century, despite Mozaffar ad-Din Shah’s signing the Constitutional Decree on August 5, 1906, unrest and conflicts persisted throughout the country. Consideringly, the south of Iran faced more challenging conditions due to its distance from the center of power. These neglected regions fell under the control of tribal chiefs who acted independently and oppressively. This resulted in lots of injustice and oppression against people. Using a descriptive-analytical method and relying on documents and library resources, this chapter investigates how the tribal and clan systems of the ports and islands in the Persian Gulf influenced the situation in these areas during the first half of the twentieth century. It further examines the consequences of Reza Shah Pahlavi’s policies in these regions. The findings indicate that during the late Qajar period, lack of significant presence of the central government in southern shores led to the unrest and intractable actions by the tribes. The situation deteriorated further after the outbreak of World War I. Economic stagnation in the ports and islands, along with the trade routes blockage and inserted conflicts and oppression by the tribes, forced many people to flee to the other regions, particularly the southern shores of the Persian Gulf. This trend continued during Reza Shah’s reign, with the central government’s exertion of power leading to a continued decrease in population of these areas.