The main reason is the victory of the Islamic Revolution.

Causing events:

1. Islamic Revolution:

In 1951, Mohammad Mossadegh became the democratically elected prime minister of Iran and took over the oil held by the United States and Britain. The resources were nationalized and owned by the Iranian people.

How could Britain and the United States allow their own interests to be harmed in vain? Therefore, the British MI6 and the US Central Intelligence Agency jointly launched an "Ajax Operation" and successfully overthrew the Communist Party in 1953. Mossadegh was elected president and King Pahlavi returned to power.

After coming to power, Pahlavi announced the implementation of the "White Revolution", carried out reforms in accordance with the American blueprint, suppressed domestic religious forces, and also signed the extraterritorial rights of American military personnel in Iran.

At that time, Tehran had become a metropolis of Western culture, with women wearing Westernized clothes and large Coca-Cola billboards standing everywhere. This caused extreme dissatisfaction among ethnic and religious people.

A large-scale mass movement against the king began to break out in Iran. The government dispatched military and police to suppress it. In Tehran, tens of thousands of demonstrators were killed.

In 1979, religious leaders launched The Islamic Revolution, large-scale demonstrations and strikes across the country, traffic disruptions, the Iranian military declared neutrality, Pahlavi was forced into exile, and the Pahlavi dynasty fell.

2. The United States and Iran severed diplomatic relations

On April 1, 1979, Khomeini announced that the country would be renamed the Islamic Republic of Iran. A referendum was held and a system of theocracy was established.

In October of the same year, news that the exiled King Pahlavi went to the United States for treatment of lymphoma was spread back to China. Angry Muslims in Tehran stormed into the U.S. Embassy and detained the embassy staff. Since then, the United States and Iran Break off diplomatic relations.

The hostage crisis began on November 4, 1979, and lasted until January 20, 1981, a period of 444 days.

The movie "Escape from Tehran" tells the story of the Iranian hostage crisis.

Extended information:

U.S. sanctions against Iran:

Reuters stated that in order to curb Iran’s missile and nuclear programs and weaken Iran’s influence in the Middle East Trump announced his withdrawal from the Iran nuclear deal in May, restarted sanctions on Iran and Africa's energy sector in August, and now announced new sanctions, trying to use a series of "combination punches" to make Iran finally surrender.

The U.S. Department of the Treasury issued a notice saying that from the 5th, it will impose sanctions on more than 700 individuals, entities, aircraft and ships involved in Iran’s finance, shipping, aviation, energy and other fields, including 50 Iranian banks and Its domestic and foreign branches, Iran’s state-owned airline and its 67 aircraft and the Iranian Atomic Energy Agency.

The sanctions focus on Iran’s oil exports. Iran's oil reserves rank fourth in the world and it is the third largest oil producer in the Organization of the Petroleum Exporting Countries after Saudi Arabia and Iraq. According to Trump, the sanctions are to "force Iran's oil export revenue to zero" to limit Iran's involvement in Yemen, Syria and other countries, and to force Iran to agree to renegotiate the nuclear issue.

In addition, US Secretary of State Pompeo announced on the 5th that the United States will temporarily allow eight countries or regions to continue to purchase Iranian oil after US sanctions on Iran. These countries or regions include: China, India, Italy, Greece, Japan, South Korea, Turkey and Taiwan. The exemption period is only 180 days and will not be extended after expiration.

It is also reported that in order to show off his tall image, when Trump announced new sanctions on Iran, he imitated the "Winter is Coming" scene in the American TV series "Game of Thrones" and posted it on Twitter A poster image. In the picture, he is walking out of layers of fog, with the words "Sanctions are coming, November 5th."

In response, the US television network HBO, the producer of "Game of Thrones", quickly stated that it "does not want the trademark to be used for political purposes." Next, American netizens took turns competing for pictures, using the same base map to draw "The lawsuit is coming" and "Mueller is coming" (Note: Miller is the special prosecutor responsible for investigating the Trump team's "Russia scandal"), and even "Prison is coming."

People's Daily Online: US sanctions take effect, Iran takes advantage of others

Baidu Encyclopedia: 1953 Iranian Coup

Baidu Encyclopedia: Iran Hostage Crisis

Baidu Encyclopedia: Escape from Tehran