Joint Comprehensive Plan Of Action. Iran is a radical Theocracy run by Rouhani, whose ultimate plan is to conquer the middle east, bring back a Persian empire of sorts, and wipe out Jews. (As far as treatment of the LGBTQ community in Iran, homosexuality is illegal and imprisonment or death penalties can be faced.) Because of this, the U.S. put sanctions on them years ago as a method to prevent them from becoming strong enough to cause massive damage. Obama made the JCPOA where he removed the sanctions on Iran plus gave them 400 million dollars. Iran gladly took the 400 million and used it to fund terrorism across the middle east. They have armed and trained groups to attack Israel, Bahrain, Kuwait, Saudi Arabia, Yemen, and just recently the U.S. embassy in Iraq. Iran has mostly been doing this with missiles instead of conventional military. They've been trying to create massive stockpiles of ballistic and nuclear missiles. In response the U.S. increased support for Israel and other friendly Arab nations, thus creating a proxy conflict, otherwise known as a cold war. Trump undid the JCPOA, put them back on sanctions, and used other pressure tactics to try to coerce them to halt their production of uranium. Israel assassinated their top nuclear scientist recently. Both are effective measures to slow their advances but after they heard Joe Biden is becoming president and he plans on returning to the JCPOA, they're not afraid of the U.S. anymore so they amped back up on uranium and missile production.
https://www.heritage.org/2021-index-us-military-strength/assessing-threats-us-vital-interests/iran