The situation is very different. If a war starts up with North Korea, millions of South Koreans will die within the first few hours (and Seoul would be complete

The situation is very different. If a war starts up with North Korea, millions of South Koreans will die within the first few hours (and Seoul would be completely wiped off the map). Nuclear weapons are an issue, but even a half-dozen or dozen nuclear warheads is insignificant in comparison to the conventional warfare bloodbath that would result if war broke out. Iran's position is much different for many reasons. 1. When things really heat up, Iran will block the Straight of Hormuz like they always do. While the US isn't using Arab oil anymore, India, China, South Korea, Japan, and much of the rest of Asia get their oil through that straight. They'll be more than happy to have the US intervene (reducing political fallout). 2. A war in Iran won't have the same worldwide economic impact as the demolition of South Korea (and perhaps Japan). During the Iran-Iraq war, the Iranians attacked US Navy ships escorting transport ships. The US destroyed or disabled most of their navy in one day in retaliation. It won't be that easy next time, but the world economic fallout can definitely be managed (this gets even better for the US if the pipeline across Saudi Arabia is finished by that time). 3. Israel is a nuclear power and is very likely to react to Iran's nuclear program progressing too far (other nuclear powers like Pakistan or India might also feel threatened). Getting involved before that point could reduce regional tension. 4. The Iran/Saudi Cold War is a proxy war between the US and Russia. The US can't afford to lose and only Iran having nuclear weapons would greatly change the power balance in favor of Russia. 5. If the US will have to go to war with Iran anyway, it's better to start things before nuclear weapons are a involved. The big issue is that Iran has ties with Russia. Saudi Arabia has close ties with the US. In turn, those two countries are involved in a regional Cold War. The US can't afford to lose to Russia, so they build military bases and posture. There is more aggression to Iran than there was to Russia simply because Iran doesn't have the threat of mutually assured destruction.