In an invasion/total war scenario meant to wholly take over Iran, the only serious problem would be the potential logistical problems.
Seriously? Have you seen Iran? I took this photo of the place (looking from the Gulf Coast towards Tehran) back in February 2025.
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It's perfect terrain for defence. A handful of guys with AK47s could hold off an army at each mountain pass. And once the army finally breaks through, there's another. And another. And another.
And the defenders know how to sneak around and attack your flanks, rear, and logistics train once you get past each ridgeline.
Russia discovered in the 1980s in Afghanistan that terrain like this is impossible to attack and hold, even when you have overwhelming logistical and technical dominance.
Then the US discovered the same, also in Afghanistan.
Iran is Afghanistan, only harder, and with more and better equipped locals who are even more fanatical in their hatred of America.
If you think "potential logistical problems" would be the
only serious problem, then you have a lot of very serious problems, the first of which is "severe overconfidence".