Israel attacking Iran: Middle East at War

Would Israel attack Iran, then what would be the consequences?
Israel’s actions both in Lebanon and Gaza in recent years indicate a military force savagely trained to kill and destroy in parallel with brutality of Genghis Khan. Israel preemptively attacking Iran may be based on assumption that a reprisal by Iran would not be serious and of very short duration. In addition, the world opinion would be changed very rapidly to other issues. Israel’s past two attacks on Iraq and Syria would support this assumption.
Israel’s second assumption is that USA, France, and England will not let Israel to lose the war. Yes, Israel may attack Iran. But would USA join in and support Israel as she did for Sadam Hossein? What would be the consequence of this attack?
First of all it will unify the Iranian people in one voice against Israel and USA, count on it.
Second, the attack will not stop there; it will drag the entire region into an anti-American union against USA-England-France and Israel.
The attack will create a very powerful force of dedicated people with one purpose to remove Israel and USA from the region. The attack will be seen as a coordinated attack by USA using Israel as a surrogate.
The attack of Sadam Hossein on Iran consolidated Iranian and their government into a united force after1979 revolution. USA must think through the long term implication of a foolish attack on Iran before removing the leash from Israel. We have been at war in both Iraq and Afghanistan for about 7 years; count on a regional war for half-century. USA has been paying the price for our 1953 attack on the Iranian nation.
Is USA ready for the consequences of Israeli attack on Iran?

Iran, is not an "existential threat" to Israel now! But, Israel should consider the consequences of attacking Iran.