An initial thought on Ahmadinejad's letter to Bush. When he says this, he is calling Bush to accept Islam -- since in traditional Muslim belief it is only Islam that guarantees "monotheism, worship of God, justice, respect for the dignity of man, belief in the Last Day."
Do you not think that if all of us come to believe in and abide by these principles, that is, monotheism, worship of God, justice, respect for the dignity of man, belief in the Last Day, we can overcome the present problems of the world – that are the result of disobedience to the Almighty and the teachings of prophets – and improve our performance? Do you not think that belief in these principles promotes and guarantees peace, friendship and justice? Do you not think that the aforementioned written or unwritten principles are universally respected? Will you not accept this invitation? That is, a genuine return to the teachings of prophets, to monotheism and justice, to preserve human dignity and obedience to the Almighty and His prophets? Mr President, History tells us that repressive and cruel governments do not survive.
In a Hadith, Muhammad tells his followers to call people to Islam before waging war against them:
Fight in the name of Allah and in the way of Allah. Fight against those who disbelieve in Allah. Make a holy war…When you meet your enemies who are polytheists, invite them to three courses of action. If they respond to any one of these, you also accept it and withhold yourself from doing them any harm. Invite them to (accept) Islam; if they respond to you, accept it from them and desist from fighting against them….If they refuse to accept Islam, demand from them the Jizya [the tax on non-Muslims specified in Qur’an 9:29]. If they agree to pay, accept it from them and hold off your hands. If they refuse to pay the tax, seek Allah’s help and fight them. (Sahih Muslim 4294)
In light of that, this letter could be -- but is not necessarily -- a prelude to an attack.