Just nuke the Oil fields!
Iran is a central-planned state and ~50% of the state's budget comes from Oil. What are they going to do without it? Increase taxes massively? Cut expenses massively? Get into massive debt? Or let Iranians start starving to death like North Koreans, instead of following the Nobel Peace Prize winner Muhammad Yunus example?
It's the same with Russia. If you destroy Russian energy (Oil+Gas) fields and make them radioactive for decades to come the Russian state dies, there's nothing but Oil & Gas on the Russian GDP & Budget.
Who needs an "invasion"? All you need are a few B-2 Spirits with long-term radioactive nukes to reach their target, they don't even have to RTB if that's necessary - the volunteer crew can parachute over water or neutral countries.
Only North Korea is safe from this threat and counter-attack since there's nothing left to be destroyed in North Korea that Kim hasn't already destroyed himself.
EDIT:
http://www.imf.org/external/pubs/ft/...06/cr06129.pdf
^^^ They can destroy Israel and attack the USA, but Israel and the USA can destroy the Iranian state. Is Israel worth your downfall Khamenei? Of course, knowing people's greed and lust for Oil, nobody will dare to destroy them. Pitty, we could use learning to live without it.