1. America is a continent. You probably mean the USA.

2. What the US has been working to stop Iran from is being independent of its near-control - which it had gained with the 1953 CIA-fomented coup d'etat against the Mossadegh government, and lost again in 1979 when the Islamist-headed faction of the rebellion gained power. While it's true that the US would not like Iran to have nuclear weapons, that has served more as an excuse to try and suppress it rather than actual motivation.