i posted this a few days ago. So here we are.
edited it for reasons: Point 2 and 3 is about the invasion corridor
An aerial war would be a completely different number from the Iraq invasion of 2003. An aerial war would certainly not bring the desired "regime change". We know very well since the Second World War that strategic aerial warfare can put pressure on a regime by destroying infrastructure and disrupting or stopping military operations, but aerial warfare strengthens a regime politically. This is sometimes forgotten again, but rather in political discourse. Militaries have this lesson pretty much on screen.
The situation with Iran today is not comparable to Iraq 15 years ago for a variety of other reasons.
Military and foreign policy differencesThe army is in a strategically different situation: reforms and repositioning make a major operation difficult, after 18 years of "War on Terror" the troops are exhausted, understaffed and often not trained for Combined Arms.
there is no invasion corridor: Iraq and Afghanistan are not participating. Iraq and Iran are often closely linked. Not to lead the Iraqi government so closely from the USA that an attack could be launched effortlessly from there. Afghanistan's infrastructure is too isolated for a deployment. Turkey does not want war with Iran and has only a very narrow border, measured by the size of Iran; the same applies to Pakistan. With just three highways in very rugged terrain, the invasion corridor through Northern Iran is very unfavourable. For obvious reasons, Russia is not a deployment area, as are the states of the South Caucasus and Turkmenistan. An amphibious invasion over the Persian Gulf would remain. Probably politically the most feasible variant, but militarily the stupidest. One heads directly towards the province of Bushehr, which not only has a strong fleet presence, but is also well equipped militarily. The terrain is initially good tank terrain - desert - but after a narrow strip changes into rugged low mountain range. Further east, near the Emirates and the Omani exclave, one would approach the Hormozgan province. There the flat coastal strip is even narrower.
Iran is basically a bad country for invaders. The state is twice as populated as Iraq and four times as big. In addition, the country consists mainly of highlands and mountains, along with deserts. The infrastructure is solid, but natural waterways that simplify logistics and advances are rare. The coasts of the Gulf offer no gateway into the interior, the country is neither easy to cross from east to west, nor from north to south. Decades of isolation and previous isolation from major trade routes and networks have left Iran poorly connected with its neighbours. Neighbours, however, had little to offer the country: The country is therefore largely networked for its own needs.
In military terms, Iran is not only a regional power, but probably the strongest power in the Middle East. The reasons are the 35 years of embargoes and the long Iran-Iraq war. During this time, the country had to defend itself against an enemy that was supplied militarily from all sides - East as well as West - while itself was cut off from supplies for mostly Western weapon systems. Not that Iran's weapons are all state-of-the-art, but Iran is largely self-sufficient. Otherwise, there are good connections to North Korean weapon forges that can supply their own products and copies of Chinese (and Soviet, or Russian) systems. A total of 500,000 soldiers are at the country's disposal, which would have to amount to an invasion force of not less than two million if one wanted to win a land war. For a subsequent occupation phase, one would probably have to reckon with quantities similar to those in Germany after the Second World War. Who should do that?
This brings us to the crucial point: there are almost no willing allies. The states of the region do not want war with Iran. None. Saudi Arabia maybe but not in the first line. Because no state could defeat, occupy and pacify Iran. And every form of invasion would cause an immense resistance movement by the indoctrination (and history) of the Iranian population. All potential allies of an invasion are either former colonial powers (Russia, UK, France and especially Turkey), Jews, Sunnis or the USA itself. No one can credibly claim a morally superior position there - as in Germany after the Second World War or in the last war in Iraq.
Not only are there almost no allies, there are also plenty of strategic opponents: Russia and China would rightly scourge the attack and they would probably support Iran at least covertly. Russia has logistically very broad possibilities to supply Iran. On the one hand indirectly through allied states on Iran's northern border (Caucasus and Turkmenistan) and on the other hand directly via the Caspian Sea. All this would be a) presumably on the margins of allied means to stop air strikes and b) an attack with Russian victims would be an escalation that Russia itself would be welcome to escalate. It would be quite enough if Russia moved a few SAM batteries near the border and actively lit and fired at allied aircraft. This could even be exploited twice and "as a sign of good will" associations could be withdrawn from Europe. This would further soften the narrative of the aggressor Russia, remove Europe from the USA and drive it away to Russia and directly endanger NATO. China could, however, not only supply endless material via Russia, but also offer its reconnaissance capacities. A little economic pressure - more subsidies for coal, steel, aluminium, export duties on electronic goods - and the US economy is going to the toilet.The peace dividend has been used up, the "Coalition of the Willing" has disappeared, Russia is once again a serious strategic opponent, China is clearly more present internationally and the USA has long ceased to be the undisputed and self-confident "leader of the free world".
Domestic political differences:
1.Trump is not George Walker Bush and the USA today are not the USA of 2001.
2.Trump differs from GWB in measure. Bush had good reasons to listen to his advisors and quite a few saw in the politics of Cheney and Bush junior a continuation of the politics of Bush senior and Cheney ten years earlier. Trump has nothing to tie in with. What he wants above all is positive feedback from as many sides as possible. A war of invasion would be highly unpopular in the USA simply because it would bring tens of thousands of coffins with it. Not to mention the costs and the foreign policy fallout. Even those guys in T_Donald are against a war.
2.After 9/11, many in the USA liked to believe that the dictator, who had been compared to Hitler in the media ten years before, could also have something to do with 9/11 or wanted evil for the USA. After all, Iraq was bombed the whole time, so the idea was not completely absurd. That made a mood for the invasion possible. The Iraq war was in the media above all a war against Saddam and for more democracy in the MENA region. A war in Iran could stand for more democracy and against Islamist terror, yes, but after the disaster in Iraq the democratization of other countries is simply no longer so popular in the USA. On the contrary: Trump was chosen for his isolationist tones and he is probably convinced of them himself. He likes to make the Fat Maxe, but he doesn't like to commit himself. And it is also clear to him that an invasion with practically all active associations - as if that were ever possible logistically - cannot be reversed as easily as a piece of paper cancels a treaty.
In the end, there is no way for any form of ally, as conceivable or imaginable, to bring an invasion of Iran to a victorious conclusion. We don't even have to talk about the occupation period afterwards. That has already failed in the two neighbouring countries Iraq and Afghanistan. Worse still, an invasion would be foreign policy suicide for the USA. It would certainly harm NATO in Europe and help Russia only at every turn. And in domestic politics an invasion requires so much "commitment" that it's out of the question. I don't even discuss the domestic consequences because I don't think there would be a majority in either chamber.
A pure air campaign, however, will not bring a solution in the form of a regime change. At best, this could eliminate strategic objectives by destroying research facilities, factories and command centres. However, this will also be a problem under international law, for as long as Iran receives confirmation from Europe, Russia and China that the conditions are being met, there will be no international consensus on punitive action. But this is precisely what makes the difference between "operations" in Kosovo or Iraq and "wars of aggression" against Ukraine and Georgia. In short: A unilateral attack on Iran would be the loss of American claims to enforce an international peace order corresponding to an international consensus.
My analysis is that one cannot achieve a regime change by a conventional war with subsequent occupation (the lack of troops and allies as well as the danger of intervention of strategic opponents) or limited air strikes. Military options to force the current government to change course do exist, although these military options should only be part of a larger sheet of power projections.
An Iranian-American conflict, however, is only superficial in the sense of Russia. The game would be easy for the USA to see through and would also be flagellated by American allies. The conflict would be extended and the world economy burdened.