Relations between Iran and the United States have always been frigid or antagonistic in nature since the Islamic Revolution. But during the past 45 years, some Iranian reformist officials have been trying to de-escalate tensions and normalize relations with the United States of America. In this study, five milestones of Iran’s détente policy have been examined. These cases include Iran's mediation in freeing the American hostages from Lebanon, Iran's lucrative economic offer to the American Conoco oil company, Iran's intelligence assistance to the US in Afghanistan for fighting against terrorism, introducing the so-called "Grand Bargain" proposal to negotiate and settle all the bones of contention with the United States, such as supporting Hezbollah and Iran’s presence in Iraq, etc. In this study, by using the method of "Process Tracing" and by analyzing the primary sources such as the US congressional records along with the IAEA reports, the influential factors in these cases were discussed in detail, and finally, the reverse results or futility of each of these measures were stated in the words of the American officials. The analysis of the détente cases confirmed the theory of "Empire, Client, Enemy States", proving that rapprochement from Iran, which is considered enemy state for the US, whether it is strategic, political or economic, will fail until the basic internal power arrangements in Iran and the nature of the Islamic Revolution alter and Iran's role towards the United States changes from an enemy to a client state.