Apart from the rule of Agha Mohammad Khan, the Qajar rule is characterized as a century of misrule. The inability of Qajar Iran’s government to maintain the country’s sovereignty during and immediately after World War I led to the British directed 1921 Persian coup d’état and Reza Shah’s establishment of the Pahlavi dynasty. Reza Shah, became the new Prime Minister of Iran and was declared the new monarch in 1925.
In the midst of World War II, in June 1941, Nazi Germany broke the Molotov–Ribbentrop Pact and invaded the Soviet Union, Iran’s northern neighbor. The Soviets quickly allied themselves with the Allied countries and in July and August, 1941 the British demanded that the Iranian government expel all Germans from Iran. Reza Shah refused to expel the Germans and on 25 August 1941, the British and Soviets launched a surprise invasion and Reza Shah’s government quickly surrendered. The invasion’s strategic purpose was to secure a supply line to the USSR (later named the Persian Corridor), secure the oil fields and Abadan Refinery (of the UK-owned Anglo-Iranian Oil Company), and limit German influence in Iran. Following the invasion, on 16 September 1941 Reza Shah abdicated and was replaced by Mohammad Reza Pahlavi, his 21 year old son.
During the rest of World War II, Iran became a major conduit for British and American aid to the Soviet Union and an avenue through which over 120,000 Polish refugees and Polish Armed Forces fled the Axis advance. At the 1943 Tehran Conference, the Allied “Big Three”—Joseph Stalin, Franklin D. Roosevelt, and Winston Churchill—issued the Tehran Declaration to guarantee the post-war independence and boundaries of Iran. However, at the end of the war, Soviet troops remained in Iran and established two puppet states in north-western Iran, namely the People’s Government of Azerbaijan and the Republic of Mahabad.
This led to the Iran crisis of 1946, one of the first confrontations of the Cold War, which ended after oil concessions were promised to the USSR and Soviet forces withdrew from Iran proper in May 1946. The two puppet states were soon overthrown and the oil concessions were later revoked.
1951–1978: Mosaddegh and Shah Mohammad Reza Pahlavi:
In 1951, Mohammad Mosaddegh was appointed as the Prime Minister.
He became enormously popular in Iran after he nationalized Iran’s petroleum industry and oil reserves. He was deposed in the 1953 Iranian coup d’état, an Anglo-American covert operation that marked the first time the United States had participated in the overthrow of a foreign government during the Cold War.
After the coup, the Shah became increasingly autocratic and sultanistic, and Iran entered a phase of decades-long controversial close relations with the United States and some other foreign governments. While the Shah increasingly modernized Iran and claimed to retain it as a fully secular state, arbitrary arrests and torture by his secret police, the SAVAK, were used to crush all forms of political opposition.