On November 4, 1980, a group of Iranian revolutionary students occupied the U.S. Embassy and strongly opposed the hostile and aggressive U.S. policy toward the Iranian nation. After students at the University of Tehran took over the embassy, documents were found revealing U.S. involvement in a coup against the democratically elected government and many other cases of espionage plots.

After the hostage crisis, Iranian students made two conditions to the United States, and if the United States could meet them, the hostages would be released. Two conditions are: the repatriation of the Shah of Iran, who fled to another country, to Iran to be tried for the crimes committed against the Iranian nation;
The United States rejected both demands.
That year, Iran's assets were about $12 billion, including $3.518 billion in deposits with the Central Bank of Iran at Bank of America in London, $400 million in deposits with Bank of America at Paris, $167 million in deposits with U.S. banks, $300 million from other Iranian banks to U.S. banks, $407 million from Petro-Iranians, $2.108 billion in funds related to oil sales, $1.1 billion in deposits from the Central Bank of Iran to the Banks of the Federal Reserve, $269 million from the Central Bank of Iran to the Banks of the Federal Reserve, $800 million in trust funds from the Iranian Ministry of Defense, and the equivalent of 1632827 ounces of gold provided by the Central Bank of Iran and the Federal Reserve Bank.
However, the Carter administration not only ignored this warning, but also took bullying action, ordering the freezing of all Iranian assets held by U.S. banks.
The executive order restricts the transfer of any property of the Iranian king and Iranian assets held by the U.S. Treasury department and banks, prolonging the hostage crisis. The two countries exchanged several letters on the matter, however, even after Iran released the hostages, the United States did not abide by their agreement, lifting restrictions on Iranian assets held in the United States. Even Iran's lawsuits in London and Paris against U.S. banks holding frozen assets have not been heard in court.
The president of the United States felt that an apology would make him look like a weak appeaser. As a result, he froze Iranian assets and stopped importing Iranian oil.
Therefore, the occupation of the U.S. embassy is the only means by which Iran demands the repatriation of funds. After the embassy staff were released, the two countries negotiated for years on iran's assets freeze, the United States did not take specific action, and there was no agreement between the two countries.
The United States and the European Union have imposed harsh sanctions on Iran under the pretext of the hostage crisis and other allegations against the Islamic Republic of Iran to justify the refusal of the United States and the European Union to return Iranian assets to Iran.
At present, the amount of frozen assets in Iran has increased to $79.2 billion as a result of new freezes on oil revenues, Iranian foreign investments, amounts frozen in court disputes, etc. since 1980. The money was deposited directly on U.S. territory or had been ordered by the U.S. to freeze in different parts of the Western world.
In July 2015, Iran and P5+1 reached an agreement and drafted a joint action plan in which the United States agreed to unfreeze Iranian assets as part of the deal. That could mean returning a portion of the billions of dollars to Iran. But the repatriation does not include the $12 billion initially held after the 1979 revolution and other assets still disputed on U.S. soil. By the time the deal goes into effect, only $29 billion will be paid, and the rest of the assets will remain frozen.
Over the past 41 years, the United States has proven that it can violate the agreement under any possible pretext. Moreover, since discussing the possibility of unfreezing Iranian assets, the release date and value of those assets have been disputed, taking into account the interest and dollar value after 42 years.
As a result, the United States has frozen the assets and property of the Iranian state in an unforgivable way, held it for 41 years, and imposed harsh sanctions to weaken Iran's economy, all of which affect ordinary Iranians.
The United States has long argued that freeing up money would make Iran appear more belligerent in the Middle East, when in fact, Iran has not attacked any other country in more than two centuries. In addition, Iran spends only $15 billion a year on military spending, while the UAE or Saudi Arabia spends $23 billion, with a military budget of more than $80 billion in 2014.