The pro-Israel lobby.
I'm going to have to dispute that. Israel has been a US ally in the region since it was founded. They need no lobby to maintain political support in the US.
Anyway, the Iran issue is, like most issues in geopolitics, very complex. I'll try to see if I can quantify this.
Reason #1: HistoryIt all starts at
Operation Ajax. The CIA and M16 collaborated in backing anti-communist rebels in Iran, who overthrew their democratically elected government and installed the
Shah's authoritarian and absolute (but most importantly, anti-USSR and pro-USA) government. Unfortunately, the Shah was
not that good of a ruler, as dictators often are. Eventually, the exiled but popular Ayatollah Ruhollah Khomeini returned to Iran and,
well... you probably know the rest of that story.Operation Ajax told an entire generation of Iranians what they were to expect from the West: The overthrow of democratically elected leaders and the exploration of their people if it served the West's greater interests in dealing with the spread of communism. This bad impression on an entire people's cultural identity would boil over years later and lead the Iranians to the theocratic government they have today.
Not a good start.
Reason #2: Iran's AlliesIran and North Korea
are on good terms. Not the best thing for ever reconciling with the United States, given that Americans generally despise the governments of both nations. Oddly enough, this antipathy generally does not extend to the actual people of the nations in question in both cases. The North Koreans are just kind of sad in how badly things are for them, and polling data shows that Iranians and Americans both highly disapprove of each others
governments....but not much else.
The other, much larger problem with Iran's allies is the relationship between
Iran and Russia. Putin loves trying to expand his power base on the world market, and causing problems for the USA with nations that are openly hostile to us is a golden opportunity to him. It should be little surprise that he has done everything in his power to use his anti-west stance to help strengthen Iran so it will give the US even more problems.
Reason #3: Iran's EnemiesOf course, the big one is that for the moment, the United States and Iran have no official diplomatic ties and are basically in a mini-Cold War with each other. That the US supports and has always supported Israel, which Iran constantly calls "Zionist occupied territories" probably speaks for itself. There's also the interesting dynamic that Saudi Arabia opposes Iran because it is the heartland of Shia Islam, and if there's anything Saudi Arabia can't stand it's the continued existence of Shia Islam. Saudi Arabia also gets a lot of business from the US, which helps make some clearly defined lines as to whom is on who's side in this tangled web of relationships.
The most interesting thing about that is that it would technically put Saudi Arabia and Israel on the same side if war breaks out against Iran. Talk about surreal.
Reason #4: Joining the Nuclear ClubIsrael and Iran both technically do not have any recognized nuclear weapons. That Israel "does not have nukes" is the most openly silly and absolutely devious concepts on the geopolitical stage. It lets Israel dodge the pesky restrictions imposed by actually owning nuclear weapons while still holding nuclear weapons and letting everyone in the region know it. Iran is a bit more tricky. Is their program to generate power alone or is it to make a nuke? I don't think I can tell you. There is enough conflicting data on this subject that we do not have a straight answer.
All we do know is that Mossad seems rather determined to
explode the hell out of anyone in Iran who is trying to advance their nuclear program, whether it exists for peace or for war.
Oh, and remember how I mentioned that Israel loves letting everyone know that they have nukes? The
Samson Option (regional mutually assured destruction, even if Israel is the only one who ever launches) was probably intentionally leaked by Israel themselves to keep the rest of the region off of their backs. In light of this existing, Iran having nukes opens the door to Bad Things happening to Earth.
So there you have it. The situation between Iran and Israel is heating up more and more every day, and Israel wants to know that the US will back them if a hot war breaks out. Meanwhile, there are plenty of Americans who would be just fine with seeing Iran's government go down in flames. There are some bad potentials in all of this, and the only way out of it that won't end in widespread violence is a peaceful democratic revolution in Iran, and soon. I don't see that as very likely, but it's all we've got.