The reality is that if the US is serious about invading Iran, it would likely require total mobilization.
A successful ground invasion of Iran to overthrow the government, occupy the country, and pacify it enough to install a US-friendly puppet regime (i.e., Shah 2.0) would most likely require far more manpower and, in all likelihood, the return of the military draft, which Trump’s press secretary recently refused to rule out.
Even then, a full-scale US ground invasion would offer no guarantee of success. Remember, the US did not even succeed in neighboring Afghanistan, which is far more primitive, poorer, and not as well armed as Iran.
Unlike most other nation states in the Middle East, Iran (known as Persia before 1935) is not an artificial construct. By race, religion, and social history, it is a nation. European bureaucrats didn’t dream up Iran by drawing zigzags on a map. The map reflects the geographic reality of a country with natural, fortress-like mountain borders. In the east, the Roman Empire generally ended where the Persian Empire began.
Iran has powerful friends throughout the Middle East—like the Houthis in Yemen, Hezbollah in Lebanon, and various Iraqi militias—who are willing to fight.
Further, Iran is Russia’s and China’s key ally in the Middle East. A US-aligned government in Tehran could help block China’s Belt and Road Initiative from pushing farther west and potentially cut off 14% of China’s oil imports. It would also hinder Russian trade through the Caspian Sea and serve as a launchpad for destabilizing Russia from its southern flank.
In short, bringing Iran under US influence would open the door to further undermining both Russia and China. For these two great powers, Iran is strategic depth. Russia and China cannot afford to let Iran fall. So I wouldn’t be surprised to see Russia and China support Iran with intelligence, weapons, supplies, and other forms of assistance that would make the conflict even more costly for the US.
Most importantly, just look at Iran’s topography. Similarly, Switzerland’s rugged mountainous terrain has helped protect it from invasion for centuries. And Iran (1,630,848 sq km) is not just the size of Switzerland (41,291 sq km), but the equivalent of roughly 40 Switzerlands.
Faced with the bleak prospects of a successful ground invasion, the US (or Israel) could resort to using nuclear weapons.
Iran is well aware that the US or Israel could use nuclear weapons against it. It has contingency plans for that outcome to ensure the survival of its government. Iran’s plans also likely include making a dash for developing its own nuclear arsenal to be able to respond in kind.
Further, it’s doubtful that Russia and China would just sit back and do nothing if the US and Israel looked like they might nuke Iran. For example, Russia could decide to station nuclear weapons and Russian soldiers on Iranian soil as a deterrent.
Suppose the US and Israel used nuclear weapons on Iran. It would shatter the global taboo and effectively give other countries the green light to use them. Could Russia then nuke Ukraine or another part of Europe? Could China nuke Taiwan? What about India and Pakistan?