In the case of Iran, not as much a "perceived historical slight" as a humiliation that led to a pullback of American territorial influence in an area vital to the supply of sand and camels, as we all know. The overthrow of the Shah put the US on the back foot (ie Saudi A) for a couple of decades. Backing Saddam to beat Iran in the '80s didn't work, and then Saddam was left over as a damn nuisance holding the central spot needed to threaten Iran. So first stop Saddam, next stop Iran. With Syria for Israel to take out.

But the best-laid plans...