Even with all her might the USA can not take on Iran alone, and no-one else will back them. Israel in spite of her numerous nuclear weapons is not capable of defeating Iran. Russia has to much invested in Iran to allow an invasion. China depends to heavily on Iranian oil and is looking toward to being able to exploit Irans natural resourses to allow an invasion. There are too many independant countries around the world who are willing to deal with Iran for sanctions to work. Europeans can't continue sanctions for very long. One last thing, the people of the world, not the governments, but the people want Iran to help Palestinians in their quest to get out from under Israels thumb.
Israeli forces demolish illegal houses, power infrastructure in Palestinian village Aqaba (Haaretz)
from the article: Netanyahu mulls gestures toward Palestinians to keep peace talks going