Fig. 1: Iran and its Satellites
First, let's look at a Iran's military.
Their navy is crap. It is tiny (less than 30,000 men) and full of badly outdated equipment. Keeping the Persian Gulf secure depends on closing off the Strait of Hormuz. As was seen in the Second World War naval power is useless without airpower. A single plane with a single bomb can destroy the mightiest warship. What does Iran have to protect it's crappy navy? An airforce that's crap and a half. Their planes are 30-year-old hand me downs. An actual fight between US or Israeli and Iranian planes would last a day and be ridiculously lopsided. However, Iran has been testing new missile systems, and while a lot of the videos of those tests are clearly edited to make them look more competant than they really are, the addition of any kind of surface-to-air missiles does put a chinaman in the armour (oh no I didn't!*) of anyone willing to engage in aerial combat with Iran.
Onto ground troops. Iran has two official armies, the regular army and the Revolutionary Guard, and a paramilitary group called Basij. The regular army had 350,000 men in 2009 and the Revolutionary Guard had about 125,000. Basij has an active duty strength of 90,000 with 300,000 in reserve, but these are regular people who are given guns and some training and they'll fall apart and surrender at the first sign of a real fight like their equivalent in Iraq did.
Fig. 2: Operation Desert Storm (by Jeff Dahl)
Remember, the 1991 Gulf War had about 180 days of airstrikes followed by just four days of ground fighting. Saddam Hussein had the fourth largest army on the planet. He promised an attack against Iraq would be the "Mother of All Battles," and it lasted four days.
Fig. 3: Operation Iraqi Freedom (by ADuran)
The 2003 invasion of Iraq lasted 21 days and completely destroyed the Iraqi military and toppled Saddam Hussein. Since then no sane person would contemplate engaging the United States in traditional warfare - it's suicide. Iraq had a larger military than Iran and they lasted less than one month against the might of the US.
So what's the problem?
Look at the first map again. The United States has been waging war since 2001, in which time roughly 7,000 Americans are killed or missing, 47,000 wounded, untold thousands having lost their minds, and a financial cost of around $1 trillion (I remember when a trillion dollars was a lot). There is no question that an all out war between the United States and Iran would last two months tops to completely destroy the Iranian military, but then what? What does victory look like? What is the exit strategy? Will the war go on forever because of an insurgency or a quixotic attempt at nation building? Will war weary troops make mistakes? Will worn out equipment malfunction more frequently, costing lives? Will the public ever go along with it, and will Congress actually declair war this time like the Constitution says they're supposed to, not the UN or some coalition? No one knows the answers to these questions, and that's not even addressing the bigger issue.
China and Russia are very pro-Iran right now. The US can destroy Iran no problem, but China and Russia have armies of millions, state-of-the-art equipment, and nuclear weapons, plus China holds most of the US national debt. What are the odds that China will let the US go to war without crippling the US economy? And that's not even addressing yet another important issue!
Invading Iran will alienate the Iranian people who will lend their support to the Mullahs.
Fig. 4: Mahhhhkmōōd I'm A Dēēnarrr Jakēēt
About 80% of the Iranian people as of now are very pro-US and want to get rid of the Ayatolla, Ak-Ma-Deen-Er-Jad, and the whole rest of the government. They rose up in 2009-10 during the election where millions of votes were "counted" in only two hours to declair I'm A Dinner Jacket the winner by divine grace. They rose up again in 2011. Each time they've begged the United States to help them and the US said some pretty words and then went and killed Qadaffi. What will happen if there is a unilateral bombing of Iranian
̶c̶h̶o̶c̶o̶l̶a̶t̶e̶ ̶c̶h̶i̶p̶nuclear bomb factories? Chances are the people will see this in light of the previous snubs as a US attack against them and not just the government. This is especially true if it is Israel that launches the attack and not the US.
So what't the solution?
If the Mullahs get the bomb that is a game changer. They will probably not use it themselves, not at first, but they do have ties to many terrorist groups. They are building up their power, making threats to close the Strait of Hormuz, sending ships to the Suez Canal, launching missiles, and exerting influence in their neighbors. Just last year the leaders of Iran and Turkey, two countries who have been the bitterest of enemies for 600 years, got together and acted all chummy like good buddies - that's scary. It's scary because politicians don't ever put aside their differences and make peace like Jesus, they do it like Al Capone, to strengthen their own power by playing countries off of one another. The leader in stable secular governance in the Islamic world is now good friends with their oldest enemy and one of the most repressive theocracies on the planet. The Mullahs believe that dying in war against infidels is a career promotion. Who's to say they won't use it to kill the Jews? Who's to say they won't give it to Hizbolla or Hamas or someone else who will in turn nuke NYC or London or Jerusalem?
What is the solution?
That's a tough one, but it will have to be one that doesn't provoke China and Russia. It will have to be one to get the Iranian people to start a revolution like in 1979, and overthrow their own government with any and all US aid necessary as long as they the Iranian people ask for it. It will have to be something that someone thinks up quick, before it's too late and the nuclear genie is let out of its bottle.
*Yes, it's an ESPN, Jeremy Lin, Max Bretos, Anthony Federico thing. The word "chink" as a derogatory term for Chinese people was first used in 1890 and the phrase "chink in the armour", which was used 3,000 different times on ESPN without drawing ire, gained widespread usage in the mid 1600s. Of course, all those people in the 1600s were horrible racists and should have been fired from their jobs. I don't watch ESPN anymore, nor will I until they apologise, rehire Federico, give him and Bretos 6000% raises, and then whoever decided to punish them has to commit suicide in proper Japanese fashion, with a dagger to the gut. It's only fitting since they like to inject racism where it doesn't exist.