The geopolitical rivalry between the Gulf Arab states and Iran has its origins in the interwar period, the period between the Paris Peace Conference in 1919, which marked the end of the First World War, until 1941 when the Persian Gulf became a theater of the Second World War. The interwar period was a formative period because it marked a transition from a Gulf society characterized by symbiosis and interdependency to a subregion characterized by national divisions, sectarian suspicions, rivalries, and political tension. The introduction of Iranian nationalism to the Persian Gulf waterway, islands, and littoral and the unprecedented interventions of the British government in the Arab shaykhdoms including Kuwait, Qatar, Bahrain, Dubai, Abu Dhabi, Sharjah, and Ras al-Khaimah, constituted a watershed in the history of the Persian Gulf, disrupted centuries of unrestricted movement, refashioned frameworks of exchange between the two shores, and forged an acute Arab-Iranian dichotomy that would characterize the Persian Gulf into the twenty-first century.