There are many reasons but we focus some main points; such as:
Nuclear program: The West and Iran have been at odds over its nuclear activities for a long time. The West suspects Iran of making nuclear bombs, but Iran denies this. Recently, there have been new attempts to bring back the 2015 nuclear deal, which would ease sanctions on Iran if it limits its nuclear activities.
Human rights: Iran has a bad reputation for human rights. The government has been criticized for crushing opposition, jailing critics, and disrespecting the rights of women and minorities. Recently, there have been demonstrations in Iran against the government’s economic policies.
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Foreign policy: Iran is a key actor in the Middle East. The country has backed various groups in the region, such as Hezbollah in Lebanon and Hamas in Gaza. Iran has been involved in the Syrian civil war.
Terrorism: Iran has been blamed for supporting terrorist groups, such as the Lebanese Hezbollah and the Palestinian Hamas. It is also said that Shiite militias in Iraq and Syria have been trained by Iran.