Well, first it was "occupying" Saudi Arabia (although we were there at the behest of the Saudis - and the British have been providing security and weapons to the Royal House of Saud for far longer than we); then it was because we oppressing the Palestinians (although we've been providing them millions of dollars every year); then it was because we were corrupting them with our wicked ways (although they've been buggering little boys and raping girls for sport much longer than we have). To be honest, I don't remember all the little ways we've offended them, but if you want to research the "justifications" Al-Qaeda and other RIFs have posted over the years, I'm sure you can find more.
It all boils down to our support of Israel anyway, so the reason of the day isn't really important.