For a long time, nations have attempted to improve their military capabilities. In the twentieth century, scientific advances in military equipment increased the power of destruction, including harm towards innocent civilians. Hence, international organizations tried to establish limits for unconventional military equipment such as the destructive power of nuclear technology. Meanwhile, countries led by radical or extremist religious governments pose a more significant threat to world peace. After Iran's efforts to acquire technology for weapons with nuclear capabilities became public, the need to stop and prevent these programs has been a priority.
A religious revolution in 1978  changed Iran from a monarchy to an Islamic state with destructive policies for all countries in the Middle East and the world. The government took an aggressive stance by imposing religious laws and enmity with the West based on religious ideologies and beliefs. The Iranian state even became an immediate threat to its neighbors. The Iranian state called on the people of the Middle East to rise against their governments and went to war with Iraq for eight years. This resulted in further restrictions on civil liberties, strengthening military forces, and increasing weapons of mass destruction. After the end of the war with Iraq, Iran always tried to create a balance of power through non-compromise or constructive negotiations with European countries and the United States. These actions led to science and technology in Pakistan, which had nuclear weapons, and North Korea, to secretly develop nuclear raw materials used in military weapons.
Iran became a member of the International Atomic Energy Agency (I.A.E.A.) in 1958, and in 1968 signed the Non-Proliferation Treaty .
In 2002, U.S., Western intelligence services efforts led to discovering informal centers of Iran's nuclear activities .
In 2003, a statement was issued stating that Iran had cooperated with I.A.E.A. inspectors to visit its nuclear facilities and suspended centrifuges voluntarily to prove the peaceful nature of the nuclear activities. Britain and France also pledged to prevent Iran's case from being referred to the U.N. Security Council.
In 2004, Iran suspended the construction and testing of centrifuges required for enrichment and stopped manufacturing spare parts for existing centrifuges.
An agreement between Iran and France, Britain, and Germany was signed. Iran accepted as a voluntary act of confidence-building, not as a legal obligation, that all enrichment and reprocessing activities would stop and that the European Union should try to admit Iran to the World Trade Organization.
In 2006, Iranian scientists succeeded in producing a complete cycle of nuclear fuel on a laboratory scale, and Iran joined the Atomic Club. The Security Council adopted Resolution 1696, which called for a moratorium on uranium enrichment in Iran, and later Resolution 1737, which targeted most of Iran's commercial, financial, missile, and nuclear activities under Article 41, Chapter 7, of the Charter of the United Nations. The resolution was the first international legal document to identify Iran's nuclear activities as a threat to regional peace and stability. Emphasizing Article 4 of the U.N. Security Council, Tehran called the allegations undocumented and called for non-discriminatory treatment of the country's nuclear activities.
Finally, long after the change in the presidency of Iran, negotiations were formed between Iran and five world powers, including the United States, Germany, China, Britain, and Russia. The final stage of the talks was held in Geneva. Iran reached an initial agreement with the other five countries of the P5 + 1 group.
After intensive negotiations between Iran and the P5 + 1 they accepted Joint Action Plan on Iran's Nuclear Program.
Under the agreement, Iran will:
1- cut off 98% enriched uranium stockpiles
2- and reduce the number of centrifuges
3- Not to enrich uranium by more than 3.67 percent
The International Atomic Energy Agency will have regular access to all Iran's nuclear facilities to monitor and verify Iran's implementation of the agreement. 
In the above cases, as mentioned, indeed, the role of the United Nations and international organizations in the implementation of international sanctions was essential and effective in negotiating with the Iranian government. Still, the U.S. government was behind all this.
The Iranian government had the support of Russia and China. Among other countries, Iran had supporters who did not comply with Iranian sanctions. Therefore, it was only with American pressure and power that Iran was forced to come to the negotiating table. Here we can conclude that REALISM has prevailed in these negotiations regarding the restrictions accepted by Iran. With the cooperation of other forces, a great power had the significant decision instead of international organizations.
 Iran and the N.P.T. January 22, 2020
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 P5+1 Countries
 The Joint Comprehensive Plan of Action (J.C.P.O.A.) at a Glance