<human>:  Why did the US agree to lift sanctions on Iran?
<bot>: The US agreed to lift sanctions on Iran because Iran agreed to curb its nuclear program. The US wanted Iran to stop enriching uranium, which is a process that can be used to make nuclear weapons. The US wanted Iran to stop enriching uranium to 20%, which is the level at which it can be used to make nuclear weapons. Iran agreed to stop enriching uranium to 20% and to not pursue nuclear weapons.