War came to Iran despite its declared neutrality. Ottoman and Russian forces attacked or occupied the northern regions, while Britain expanded its control in the south. The young king, Ahmad Shah, was ill-equipped to rule as rival political leaders emerged. American missionaries documented the devastation of war as Iran suffered from famine and the influenza epidemic. The conclusion of World War I did not bring much support to Iran as its concerns were rebuffed at the Congress of Versailles. A coup brought political change and the end of Qajar rule. The military commander Reza Khan positioned himself as the new leader of Iran, even after the political defeat of the republican movement. Tribal disarmament and state control followed the end of war and the rise of a new monarchy. After the war America considered new opportunities for involvement in Iran.

This chapter discusses Iranian nationalism during the years of Reza Khan’s rise as a nationalism rooted in territorial concepts. It describes how the emerging military rule of Reza Khan coalesced with the foreign policy efforts of the Iranian statesmen until parliamentary politics were overshadowed by the military’s arbitrary rule. Against this backdrop, the greater part of the chapter is devoted to depicting Iran's policy toward the Persian Gulf and toward the Arab shaykhdoms in the Gulf during the period of Reza Khan's rise, and the rhetoric and conduct of Iranian officials in the port towns and islands where the paths of Arabs and Iranians from different walks of life intersected. The assertion of central authority over Arabistan (renamed Khuzestan) is viewed as a decisive step in Iran’s more ambitious goal of reducing British influence in the Persian Gulf waterway, islands, and littoral.

This chapter discusses British policy in the Persian Gulf during the interwar period. A focus is placed on the way in which the British government coped with the challenges to its dominant position during key junctures of the interwar years. First it provides an analysis of how British policy evolved in relation to the emerging challenges in the region, namely the coming to the fore of Reza Khan and the consolidation of power by Ibn Sa‘ud. Then it provides an analysis of Britain’s negotiations with Iran toward the conclusion of a comprehensive treaty between the two countries. An analysis of these negotiations, which ultimately failed to produce an agreement, provides valuable insights into the positions of both governments on issues in the Persian Gulf during the interwar years. The last section sheds light on how local actors perceived Britain's role in the Gulf, an inquiry that forms a vital precursor to the topic of Arab-Iranian relations in the Persian Gulf during the interwar period.